build: Require go 1.4 or newer
build: Require go 1.4 or newer

This was actually a case for some time already, but it wasn't coded in
configure. This also cleans up the awful regexes munged by autoconf.

sstabellini/rkt,euank/rkt,mike1729/rkt,dgonyeo/rkt,sinfomicien/rkt,kinvolk/rkt,cab105/rkt,mike1729/rkt,coreos/rkt,blixtra/rkt,mike1729/rkt,Shashwatsh/rkt,kbrwn/rkt,joshix/rkt,dgonyeo/rkt,linki/rkt,euank/rkt,kinvolk/rkt,shobhit85/rkt,rkt/rkt,joshix/rkt,kbrwn/rkt,linki/rkt,markllama/rkt,nhlfr/rkt,tmrts/rkt,tmrts/rkt,cab105/rkt,monstermunchkin/rkt,jonboulle/rkt,tmrts/rkt,rkt/rkt,il9ue/rkt,kinvolk/rkt,matthaias/rkt,sinfomicien/rkt,alban/rkt,jakon89/rkt,dgonyeo/rkt,monstermunchkin/rkt,blixtra/rkt,s-urbaniak/rkt,sstabellini/rkt,s-urbaniak/rkt,yifan-gu/rocket,cab105/rkt,ybubnov/rkt,alban/rkt,Wilybald/rkt,joshix/rkt,yifan-gu/rkt,endocode/rkt,sgotti/rkt,endocode/rkt,Shashwatsh/rkt,linki/rkt,yifan-gu/rocket,lucasallan/rkt,alban/rkt,jakon89/rkt,intelsdi-x/rkt,sinfomicien/rkt,ybubnov/rkt,blixtra/rkt,intelsdi-x/rkt,jakon89/rkt,sgotti/rkt,jonboulle/rkt,nhlfr/rkt,yifan-gu/rkt,shobhit85/rkt,sstabellini/rkt,markllama/rkt,jjlakis/rkt,nhlfr/rkt,s-urbaniak/rkt,Shashwatsh/rkt,intelsdi-x/rkt,achanda/rkt,squeed/rkt,il9ue/rkt,Wilybald/rkt,ybubnov/rkt,il9ue/rkt,lucasallan/rkt,euank/rkt,yifan-gu/rkt,matthaias/rkt,rkt/rkt,Wilybald/rkt,kbrwn/rkt,lucasallan/rkt,sgotti/rkt,yifan-gu/rocket,coreos/rkt,monstermunchkin/rkt,Wilybald/rkt,coreos/rkt,jjlakis/rkt,akshaykarle/rkt,endocode/rkt,jonboulle/rkt,jjlakis/rkt,kinvolk/rkt,markllama/rkt,rkt/rkt,achanda/rkt,akshaykarle/rkt,achanda/rkt,squeed/rkt,lucasallan/rkt,squeed/rkt,akshaykarle/rkt,joshix/rkt,matthaias/rkt,shobhit85/rkt