twister: adapt ctest results for twister

When we have skips in ctest, the overall result should not be marked as
a SKIP unless all tests have been skipped. If we have passing tests,
mark the test as PASS. Any failures/errors obviously will fail the
tests.

Also pass the skip reason from ctest to twister to give a hint about
what is going on in case of skips.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>