core: Remove FormatException

FormatException was introduced in the very first git commit of oVirt,
and has not been used since.

It's safe to assume that it never will, and can safely be removed, along
with any code attempting to catch it.

Change-Id: Ie3e4351aab1f51bbc8ae6b28892ff822d7fa4467
Signed-off-by: Allon Mureinik <amureini@redhat.com>