tests/config: perfect test
tests/config: perfect test

Signed-off-by: Zhou Hao <zhouhao@cn.fujitsu.com>

Closes: #650
Approved by: rhatdan

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