Mark mtrace tests UNSUPPORTED if bug-ga2.mtrace or tst-leaks2.mtrace are missing

Starting with commit 29fddfc7, the
tests posix/bug-ga2 and resolv/tst-leaks2 are test-container tests.

If test-container.c returns with EXIT_UNSUPPORTED, the tests with
mtrace() are not executed and the mtrace files do not exist.

Therefore the "mtrace-analysis-part" of those tests are marked
UNSUPPORTED if the mtrace files are missing.

Reported-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>