Make sure cms-externals-pr-test can be still used by docker

while you are at it, may be match for ; too e.g. 
grep "SCRAM_ARCH=$SCRAM_ARCH;" | grep "RELEASE_QUEUE=$RELEASE_QUEUE;"

to match the exact queue, without it CMSSW_6_2_X can match CMSSW_6_2_X and CMSSW_6_2_X_SLHC