Post-push fix of WL#13505 which introduced the change of looking for a
default configuration change to conf-${testsuite}-autotest.cnf.

Before the change, upgrade/downgrade tests were using
conf-{up/down}grade-vigdis05.cnf as their configuration files. This
change renamed conf-{up/down}grade-vigdis05.cnf to
conf-{up/down}grade-autotest.cnf. So, according to the priority,
upgrade/downgrade fell back to use conf-{up/down}grade.cnf as their
configuration files which doesn't contain recent bug fixes. This broke
the upgrade/downgrade testing.

So, renaming conf-{up/down}grade-autotest.cnf to conf-{up/down}grade.cnf
which contains the bug fixes and is higher in priority of config files.

Approved by: Mauritz Sundell <mauritz.sundell@oracle.com>