Adjust conformance-test error-message regex
Adjust conformance-test error-message regex

Sometime around `docker.io 20.10.2-0ubuntu1~20.04.2` several error
message strings were updated from `file not found` to `file does not
exist`.  This breaks conformance testing.  Fix this by adding in
the new error message.

Signed-off-by: Chris Evich <352d8596d782a469eafa66a46434e15a449859ce@redhat.com>

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