Use pytest instead of nosetests

Nose has been in maintenance mode for the past several years
and pytest is a good replacement.

Other changes:
- Replace deprecated assertRegexpMatches with assertRegex
- Replace deprecated assertRaisesRegexp with assertRaisesRegex
- Replace deprecated SafeConfigParser with ConfigParser
- Force reinstall pytest and mock in tox virtualenv. This is because
  the globally installed packages may not work as expected(occured in
  jenkins job).

JIRA: RHELCMP-1619
Signed-off-by: Haibo Lin <hlin@redhat.com>

tests/test_compose.py

@@ -56,6 +56,7 @@ class ComposeTestCase(unittest.TestCase):
     def test_setup_logger(self, ci):
         conf = {}
         logger = logging.getLogger("test_setup_logger")
+        logger.setLevel(logging.DEBUG)
         compose = Compose(conf, self.tmp_dir, logger=logger)
         self.assertEqual(len(logger.handlers), 2)