Uniquify test names from gdb.python/{py-objfile.exp,py-pp-registration.exp}

Uniquify test names from gdb.python/{py-objfile.exp,py-pp-registration.exp}

While running some regression tests, I noticed that the two Python
tests mentioned in the $SUBJECT contain non-unique names.  This is a
violation of our guidelines:

  <https://sourceware.org/gdb/wiki/GDBTestcaseCookbook#Make_sure_test_messages_are_unique>

And also makes things harder for BuildBot.  So I hacked both testcases
and made every test name unique.  I guess this could be considered an
obvious patch, but I decided to post it before pushing because others
may have different opinions about the names.

OK to apply?

gdb/testsuite/ChangeLog:
2015-07-28  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.python/py-objfile.exp: Make some tests have unique names.
	* gdb.python/py-pp-registration.exp: Likewise.