Description of problem:
If the filename entered for --certs-tar is not correct, the installer will commence and eventually error out for confusing reasons.  We should do some sanity checking to make sure the filename passed to --certs-tar is valid before starting install.

Version-Release number of selected component (if applicable):

Satellite-6.0.3-RHEL-6-20140702.0

How reproducible:


Steps to Reproduce:
1.  On main instance, create cert for target capsule and copy to target
2.  Attempt to install capsule, but use an incorrect string for the certs.tar file, i.e. cloud-qe-4.idm.lab.bos.redhat.com-certs.tra (note the typo)
3.  View results

Actual results:
Process errors out and user has to dig pretty deep into the log to figure out why the install failed; it is not really clear that it is due to a bad value passed to --certs-tar

Expected results:
We should validate the value passed to --certs-tar before ever executing.

Additional info: