Fix coverage job to compare proper git diff and make it more strict
Fix coverage job to compare proper git diff and make it more strict

Allow only 4 lines non covered by unit tets

Currently we are testing patch against master, instead of HEAD^
which produce issue when checked commit is not after current rebase.

master
  |
patch1
  |
patch2
  |
old_master <- your_patch

Proper way to check coverage is to do diff between
your_patch and old_master instead of master.

Change-Id: Ib0a177eafa9c7dcce799bde1c6b45d541fedde05

aplanas/rally,group-policy/rally,aforalee/RRally,openstack/rally,vponomaryov/rally,amit0701/rally,openstack/rally,group-policy/rally,gluke77/rally,openstack/rally,go-bears/rally,eayunstack/rally,eonpatapon/rally,yeming233/rally,shdowofdeath/rally,cernops/rally,gluke77/rally,cernops/rally,eayunstack/rally,group-policy/rally,vefimova/rally,paboldin/rally,vefimova/rally,gluke77/rally,afaheem88/rally,vganapath/rally,go-bears/rally,vganapath/rally,gluke77/rally,vganapath/rally,amit0701/rally,vponomaryov/rally,openstack/rally,paboldin/rally,eonpatapon/rally,amit0701/rally,paboldin/rally,pyKun/rally,vganapath/rally,shdowofdeath/rally,pyKun/rally,redhat-openstack/rally,yeming233/rally,aforalee/RRally,redhat-openstack/rally,aplanas/rally,afaheem88/rally,eayunstack/rally