Allow py.test system test to skip itself

Allow py.test system test to skip itself

Enable use of shortcuts like pytest.importorskip and other tricks
which can cause test to skip itself.

(cherry picked from commit b8829c801f876b58e0ac1ce354e6790ef8de4532)

In addition to b8829c801f876b58e0ac1ce354e6790ef8de4532,
"R:$systest:SKIPPED" is not being printed when pytests are skipped
because that leads to two `R:` lines - SKIPPED and PASS/FAIL which is
determined later based on other conditions (core files identified,
assertion failures, shell test result, ...) - which is wrong and
testsummary.sh rightfully stumbles on it:

    I:Found 106 test results, but 105 tests were run