avocado.core.status: TEST_NA status is not a failure

When we skip a test, that is not a failure. Only the
test was not applicable for the given test environment.
Therefore, we should not report those as failures.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/core/status.py

@@ -16,7 +16,7 @@ This is used by methods and functions to return a cut and dry answer to wether
 a test or a job in avocado PASSed or FAILed.
 """
 
-mapping = {"TEST_NA": False,
+mapping = {"TEST_NA": True,
            "ABORT": False,
            "ERROR": False,
            "FAIL": False,