test: Avoid failing skipped tests

test: Avoid failing skipped tests

When a test returns -EAGAIN this should not be considered a failure.
Fix what seems to be a problem case, where the pytests see a failure
when a test has merely been skipped.

We cannot squash the -EAGAIN error in ut_run_test() since the failure
count is incremented by its caller, ut_run_test_live_flat()

The specific example here is on snow, where a test is compiled into the
image but cannot run, so returns -EAGAIN to skip:

    test/py/tests/test_ut.py sssnow # ut bdinfo bdinfo_test_eth
    Test: bdinfo_test_eth: bdinfo.c
    Skipping: Console recording disabled
    test/test-main.c:486, ut_run_test_live_flat(): 0 == ut_run_test(uts,
    test, test->name): Expected 0x0 (0), got 0xfffffff5 (-11)
    Test bdinfo_test_eth failed 1 times
    Skipped: 1, Failures: 1
    snow # F+u-boot-test-reset snow snow

The fix is simply to respect the return code from ut_run_test(), so do
that.

Signed-off-by: Simon Glass <sjg@chromium.org>