QPID-5520: qpid-python-test should not fail for skipped tests.

The qpid-python-test script has a facility for skipping tests (by raising a
Skipped exception) which works fine BUT if tests are skipped the script exits
with non-0 status - i.e. failure.

With this commit the script exits with a 0 exit status (success) unless there
are actual failures.

See discussion at: http://apache-qpid-developers.2158895.n2.nabble.com/qpid-python-test-script-should-skipped-tests-be-considered-failures-td7592307.html

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1562167 13f79535-47bb-0310-9956-ffa450edef68