Use simple scanner instead of regexp for etchosts.Delete
Use simple scanner instead of regexp for etchosts.Delete

Benchmark results:
benchmark           old ns/op     new ns/op     delta
BenchmarkDelete     4315186       2245829       -47.96%

benchmark           old allocs     new allocs     delta
BenchmarkDelete     4645           10             -99.78%

benchmark           old bytes     new bytes     delta
BenchmarkDelete     1590011       4832          -99.70%

Signed-off-by: Alexander Morozov <4efb7da3e38416208b41d8021a942884d8a9435c@docker.com>

flavio/docker,cpuguy83/docker,nalind/docker,konstruktoid/docker-upstream,paralin/docker,konstruktoid/docker-upstream,moby/moby,moby/moby,Ramzec/docker,AkihiroSuda/docker,bearstech/moby,cpuguy83/docker,jthelin/docker,gnailuy/docker,jimjag/docker,vdemeester/docker,yosifkit/docker,nawawi/docker,AkihiroSuda/docker,bearstech/moby,moul/docker,jthelin/docker,nalind/docker,nalind/docker,gnailuy/docker,Ramzec/docker,docker/docker,trebonian/docker,flavio/docker,jameszhan/docker,trebonian/docker,paralin/docker,thaJeztah/docker,konstruktoid/docker-upstream,yosifkit/docker,moul/docker,Mokolea/docker,konstruktoid/docker-upstream,paralin/docker,docker/docker,mahak/docker,trebonian/docker,bearstech/moby,mahak/docker,gnailuy/docker,moul/docker,flavio/docker,vdemeester/docker,djs55/docker,djs55/docker,flavio/docker,AkihiroSuda/docker,mahak/docker,jameszhan/docker,jimjag/docker,nawawi/docker,Mokolea/docker,moul/docker,thaJeztah/docker,mahak/docker,gnailuy/docker,yosifkit/docker,nawawi/docker,trebonian/docker,yosifkit/docker,thaJeztah/docker,bearstech/moby,Ramzec/docker,djs55/docker,jameszhan/docker,nawawi/docker,paralin/docker,cpuguy83/docker,Ramzec/docker,AkihiroSuda/docker,Mokolea/docker,Mokolea/docker,nalind/docker,moby/moby,thaJeztah/docker,docker/docker,vdemeester/docker,jimjag/docker,moby/moby,jimjag/docker,cpuguy83/docker