getRandomHexChars(): use /dev/urandom just to seed.
getRandomHexChars(): use /dev/urandom just to seed.

On Darwin /dev/urandom depletes terribly fast. This is not an issue
normally, but with Redis Cluster we generate a lot of unique IDs, for
example during nodes handshakes. Our IDs need just to be unique without
other strong crypto requirements, so this commit turns the function into
something that gets a 20 bytes seed from /dev/urandom, and produces the
rest of the output just using SHA1 in counter mode.

flashbuckets/redis,hawkchch/redis,izhoujie/redis,jasonkying/redis,GrimDerp/redis,saisai/redis,190235047/redis,netroby/redis,GrimDerp/redis,YuanZhewei/redis,ouyangkongtong/redis,thomasdarimont/redis,PKRoma/redis,janekmi/redis,GrimDerp/redis,nnog/redis,allengaller/redis,zguangyu/redis,cusspvz/redis,thomasdarimont/redis,hgl888/redis,4396/redis,jasonkying/redis,davidradunz/redis,simplestbest/redis,csuhawk/redis,190235047/redis,antirez/redis,YongMan/redis,spinlock/redis,davidradunz/redis,zhcy/redis,july2993/redis,CodeJuan/redis,supasate/redis,RepmujNetsik/redis,programmecat/redis,seandsky/redis,badboy/redis,dreamquster/redis,francischan714/redis,cnbin/redis,wenxueliu/redis_comment,xuguruogu/redis,rogerlz/redis,supasate/redis,hawkchch/redis,programmecat/redis,arijitvt/redis,YuanZhewei/redis,netroby/redis,GitHubMota/redis,atreeyang/redis,shreesundara/redis,Sciumo/redis,ytjiang/redis,xuguruogu/redis,charsyam/redis,LongXQ/redis,zhcy/redis,dayuoba/redis,universsky/redis,linfangrong/redis,antirez/redis,gaoxianglong/redis,xuguruogu/redis,YuraLukashik/redis,CodeJuan/redis,mcanthony/redis,ctripcorp/redis,ituncle/redis,yossigo/redis,z-fork/redis,jackyan/redis,YuanZhewei/redis,kmiku7/redis,badboy/redis,gaoxianglong/redis,charsyam/redis,wangyikai/redis,nnog/redis,pmem/redis,ofirluzon/redis,StevenTsai/redis,hawkchch/redis,zguangyu/redis,wenxueliu/redis_comment,ton31337/redis,tanghaodong25/redis,blackmady/redis,shining-yang/redis,oranagra/redis,hornen/redis,hedisdb/hedis,xlzhan/redis,Markgorden/redis,CodeJuan/redis,wprice/redis,LongXQ/redis,pcarrier/redis,ncopa/redis,AALEKH/redis,ErikDubbelboer/redis,citusdata/redis,shining-yang/redis,SummonY/redis,yossigo/redis,mgk/redis,mgk/redis,allengaller/redis,neomantra/redis,clamoriniere1A/redis,elkingtonmcb/redis,mumingv/redis,mumingv/redis,YuraLukashik/redis,YuanZhewei/redis,riyan8250/redis,cusspvz/redis,RepmujNetsik/redis,seandsky/redis,huyuezheng/redis,cloudrain21/redis,tanghaodong25/redis,mcanthony/redis,supasate/redis,cnbin/redis,flashbuckets/redis,takeshineshiro/redis,roth1002/redis,oranagra/redis,twskipper/redis,neomantra/redis,huyuezheng/redis,MasahikoSawada/redis,a-pavlov/redis,fengshao0907/redis,harrisonfeng/redis,rogerlz/redis,itugs/redis,CodeJuan/redis,tjschuck/redis,seandsky/redis,shining-yang/redis,qiyang0221/redis,simplestbest/redis,xujunhai1991/redis,riyan8250/redis,linfangrong/redis,mverrilli/redis,Aliceljm1/redis,a-pavlov/redis,duanx/redis,ton31337/redis,Markgorden/redis,sunheehnus/redis,ctripcorp/redis,zguangyu/redis,thomasdarimont/redis,ituncle/redis,pkdevbox/redis,duanx/redis,wprice/redis,PradheepShrinivasan/redis,itugs/redis,neomantra/redis,atreeyang/redis,mcanthony/redis,hgl888/redis,4396/redis,valdsJohn/redis,h0x91b/redis,vincent-vivian-liu/redis,ErikDubbelboer/redis,hornen/redis,wprice/redis,jingjidejuren/redis,JoeWoo/redis,NBSW/redis,h0x91b/redis,pmem/redis,oranagra/redis,takeshineshiro/redis,riyan8250/redis,itamarhaber/redis,simplestbest/redis,guker/redis,itamarhaber/redis,tjschuck/redis,YuraLukashik/redis,xuguruogu/redis,aim-for-better/redis,weizijun/redis,Wangyao14cyy/redis,jasonkying/redis,sunheehnus/redis,AALEKH/redis,Wangyao14cyy/redis,PradheepShrinivasan/redis,flashbuckets/redis,alenslan/redis,holstvoogd/redis,hornen/redis,ofirluzon/redis,neomantra/redis,wangyikai/redis,colstrom/redis,nnog/redis,yuhc/redis-benchmark-enhanced,timothyohare/3rdPartySrc-redis,riyan8250/redis,z-fork/redis,wbailey5/redis,NBSW/redis,davidradunz/redis,mverrilli/redis,AplayER/redis,spinlock/redis,alenslan/redis,Sciumo/redis,honestme/redis,twskipper/redis,seandsky/redis,honestme/redis,mingyaaaa/redis,july2993/redis,StevenTsai/redis,healerkx/redis,zhiliaoniu/redis,francischan714/redis,rouzier/redis,brg-liuwei/redis,StevenTsai/redis,kaushik94/redis,pedigree/redis,abhiklodh/redis,AplayER/redis,wbailey5/redis,fengshao0907/redis,a-pavlov/redis,takeshineshiro/redis,healerkx/redis,harrisonfeng/redis,hedisdb/hedis,wbailey5/redis,mingyaaaa/redis,seppo0010/redis,yossigo/redis,PKRoma/redis,kmiku7/redis,healerkx/redis,soveran/redis,jackyan/redis,pkdevbox/redis,soloestoy/redis,taoguan/redis,xujunhai1991/redis,harrisonfeng/redis,soveran/redis,yossigo/redis,jackyan/redis,Sciumo/redis,dayuoba/redis,arijitvt/redis,citusdata/redis,tellapart/redis,dayuoba/redis,csuhawk/redis,190235047/redis,ofirluzon/redis,ipmobiletech/redis,twskipper/redis,tellapart/redis,kensou97/redis,valdsJohn/redis,qiyang0221/redis,pkdevbox/redis,citusdata/redis,janekmi/redis,xlzhan/redis,duanx/redis,PradheepShrinivasan/redis,qiyang0221/redis,cloudrain21/redis,soveran/redis,brg-liuwei/redis,OmarQunsul/graph-redis,mumingv/redis,francischan714/redis,GitHubMota/redis,nuxeh/redis,alenslan/redis,neomantra/redis,ytjiang/redis,soloestoy/redis,supasate/redis,ctripcorp/redis,abhiklodh/redis,vincent-vivian-liu/redis,honestme/redis,weizijun/redis,SummonY/redis,fengshao0907/redis,Aliceljm1/redis,ton31337/redis,LongXQ/redis,huyuezheng/redis,arijitvt/redis,netroby/redis,izhoujie/redis,gaoxianglong/redis,seppo0010/redis,mingyaaaa/redis,4396/redis,modulexcite/redis,rouzier/redis,kensou97/redis,timothyohare/3rdPartySrc-redis,july2993/redis,shining-yang/redis,clamoriniere1A/redis,tellapart/redis,rouzier/redis,GitHubMota/redis,mengyou0304/redis,pcarrier/redis,z-fork/redis,taoguan/redis,francischan714/redis,vincent-vivian-liu/redis,holstvoogd/redis,mengyou0304/redis,SyntaxStacks/redis,Soledad89/redis,OmarQunsul/graph-redis,shreesundara/redis,OmarQunsul/graph-redis,LongXQ/redis,clamoriniere1A/redis,atreeyang/redis,roth1002/redis,mverrilli/redis,AALEKH/redis,modulexcite/redis,universsky/redis,cnbin/redis,badboy/redis,modulexcite/redis,xlzhan/redis,MasahikoSawada/redis,sunheehnus/redis,allengaller/redis,tellapart/redis,cloudrain21/redis,valdsJohn/redis,wangyikai/redis,SyntaxStacks/redis,devaos/redis,colstrom/redis,itamarhaber/redis,xujunhai1991/redis,aim-for-better/redis,ton31337/redis,taoguan/redis,jasonkying/redis,zhcy/redis,badboy/redis,4396/redis,brg-liuwei/redis,wprice/redis,universsky/redis,ytjiang/redis,ituncle/redis,allengaller/redis,jingjidejuren/redis,hedisdb/hedis,dreamquster/redis,Wangyao14cyy/redis,Sciumo/redis,antirez/redis,Aliceljm1/redis,YongMan/redis,flashbuckets/redis,brg-liuwei/redis,YongMan/redis,rogerchina/redis,janekmi/redis,tanghaodong25/redis,PKRoma/redis,SyntaxStacks/redis,charsyam/redis,SummonY/redis,Markgorden/redis,roth1002/redis,abhiklodh/redis,iandyh/redis,aim-for-better/redis,colstrom/redis,mengyou0304/redis,StevenTsai/redis,nuxeh/redis,hgl888/redis,programmecat/redis,ofirluzon/redis,soveran/redis,nuxeh/redis,zhiliaoniu/redis,kensou97/redis,mgk/redis,ncopa/redis,linfangrong/redis,blackmady/redis,guker/redis,kaushik94/redis,oranagra/redis,dreamquster/redis,duanx/redis,rouzier/redis,csuhawk/redis,PradheepShrinivasan/redis,NBSW/redis,PKRoma/redis,tjschuck/redis,ctripcorp/redis,Markgorden/redis,rogerchina/redis,zczhuohuo/redis,hgl888/redis,arijitvt/redis,YuraLukashik/redis,a-pavlov/redis,MasahikoSawada/redis,wangyikai/redis,ErikDubbelboer/redis,rogerchina/redis,saisai/redis,pcarrier/redis,PKRoma/redis,vincent-vivian-liu/redis,blackmady/redis,healerkx/redis,devaos/redis,linfangrong/redis,simplestbest/redis,valdsJohn/redis,csuhawk/redis,oranagra/redis,yuhc/redis-benchmark-enhanced,netroby/redis,GrimDerp/redis,zhiliaoniu/redis,SyntaxStacks/redis,iandyh/redis,kmiku7/redis,ipmobiletech/redis,JoeWoo/redis,cusspvz/redis,abhiklodh/redis,h0x91b/redis,yuhc/redis-benchmark-enhanced,cusspvz/redis,pmem/redis,saisai/redis,ipmobiletech/redis,gaoxianglong/redis,wbailey5/redis,devaos/redis,shreesundara/redis,ouyangkongtong/redis,elkingtonmcb/redis,iandyh/redis,qiyang0221/redis,guker/redis,kaushik94/redis,pkdevbox/redis,hawkchch/redis,nuxeh/redis,seppo0010/redis,RepmujNetsik/redis,JoeWoo/redis,jingjidejuren/redis,ouyangkongtong/redis,devaos/redis,ipmobiletech/redis,roth1002/redis,ituncle/redis,pedigree/redis,programmecat/redis,wenxueliu/redis_comment,tanghaodong25/redis,mengyou0304/redis,OmarQunsul/graph-redis,rogerlz/redis,soloestoy/redis,MasahikoSawada/redis,pedigree/redis,ncopa/redis,Soledad89/redis,itugs/redis,ouyangkongtong/redis,soloestoy/redis,rogerchina/redis,itugs/redis,mgk/redis,SummonY/redis,modulexcite/redis,weizijun/redis,twskipper/redis,davidradunz/redis,thomasdarimont/redis,citusdata/redis,AplayER/redis,jingjidejuren/redis,alenslan/redis,wenxueliu/redis_comment,Aliceljm1/redis,AALEKH/redis,itamarhaber/redis,zczhuohuo/redis,zhiliaoniu/redis,NBSW/redis,h0x91b/redis,zczhuohuo/redis,soloestoy/redis,clamoriniere1A/redis,pcarrier/redis,mingyaaaa/redis,kensou97/redis,kaushik94/redis,GitHubMota/redis,holstvoogd/redis,taoguan/redis,shreesundara/redis,cnbin/redis,jackyan/redis,janekmi/redis,dayuoba/redis,tjschuck/redis,seppo0010/redis,cloudrain21/redis,Soledad89/redis,Wangyao14cyy/redis,spinlock/redis,huyuezheng/redis,colstrom/redis,charsyam/redis,hedisdb/hedis,universsky/redis,yuhc/redis-benchmark-enhanced,zhcy/redis,elkingtonmcb/redis,izhoujie/redis,timothyohare/3rdPartySrc-redis,atreeyang/redis,mcanthony/redis,takeshineshiro/redis,pedigree/redis,hornen/redis,nnog/redis,rogerlz/redis,harrisonfeng/redis,Soledad89/redis,charsyam/redis,sunheehnus/redis,weizijun/redis,zczhuohuo/redis,antirez/redis,pmem/redis,honestme/redis,fengshao0907/redis,izhoujie/redis,ofirluzon/redis,blackmady/redis,holstvoogd/redis,july2993/redis,ncopa/redis,dreamquster/redis,spinlock/redis,RepmujNetsik/redis,ytjiang/redis,xujunhai1991/redis,mverrilli/redis,190235047/redis,elkingtonmcb/redis,aim-for-better/redis,YongMan/redis,AplayER/redis,z-fork/redis,mumingv/redis,xlzhan/redis,yossigo/redis,guker/redis,JoeWoo/redis,kmiku7/redis,iandyh/redis,zguangyu/redis,timothyohare/3rdPartySrc-redis,saisai/redis,ErikDubbelboer/redis