use absolute path for bundlePath
use absolute path for bundlePath

When running buildah code on Atomic Hosts, we need to make sure
the absolute path for the bundlePath is used or operations
will fail.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #745
Approved by: nalind

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