webadmin: Dialogue for attaching ISOs is not logically ordered

In install host dialog the iso's listed are not
ordered.

Use the new RpmVersionUtils class to order the
iso's in decreasing order of version and release.

Change-Id: I80cf81769e34bf66e512ada7cb2a60efe88d11ab
Bug-Url: https://bugzilla.redhat.com/1060636
Signed-off-by: Ravi Nori <rnori@redhat.com>