Use bugzilla_formatdup.conf for detected duplicates in python too. Fixes rhbz#875312.

We use bugzilla_formatdup.conf for coredump problems for some time now,
but for python bugzilla_format.conf was still used both for new bugs and
for dups. This change brings python Bugzilla reporting in sync with coredump
Bugzilla reporting.
Merge pull request #749 from abrt/rhbz875312

Use bugzilla_formatdup.conf for detected duplicates in python too. Fixes...