packagers: yum: detect failures during installation

yum does not raises an exception during process transaction if one or
more of packages return an error during installation.

So detect the error condition based on error log.

Change-Id: Icb6c927b6494f3d59ea30f8878c8cdbe21a7d8a4
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>