Work around Firebird/InterBase/ODBC crash in tests

Work around Firebird/InterBase/ODBC crash in tests

If DBD::Firebird and DBD::InterBase are used in the same process, the
last one loaded leaves an active statement handle around and later
segfaults at some point in the tests.  Also, if DBD::ODBC is used
before either of them, they leak the handle but don't segfault.

Thus, to avoid breaking installing DBIC if more than one of
DBICTEST_FIREBIRD(_INTERBASE|ODBC)?_DSN is set, skip Interbase if any
of the others are set, and make sure to run the ODBC test last.

However, keep the leak-triggering order for author, CI and smoker
runs, so we don't forget that it needs fixing.