Move the exceptions into their own file
Add a dedicated exception class for PkgDB <-> Bugzilla interaction error
In case of error in the interaction between pkgdb and bugzilla, raise a PkgdbBugzillaException
Catch exception thrown in case of error while interacting with bugzilla

In this case flash the error message and rollback the transaction

Fixes https://fedorahosted.org/fedora-infrastructure/ticket/2547