Update regex for multi stage base test
Update regex for multi stage base test

Signed-off-by: Yiqiao Pu <ypu@redhat.com>

Closes: #1172
Approved by: rhatdan

nalind/buildah-1,TomSweeneyRedHat/buildah,rhatdan/buildah,projectatomic/buildah,ipbabble/buildah,ipbabble/buildah,TomSweeneyRedHat/buildah,projectatomic/buildah,rhatdan/buildah,nalind/buildah,nalind/buildah-1,projectatomic/buildah,TomSweeneyRedHat/buildah,nalind/buildah,nalind/buildah-1,rhatdan/buildah