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>

tox.ini

@@ -36,15 +36,18 @@ deps =
     mmdzanata
     parameterized
     dict.sorted
+    urlgrabber
     mock
-    nose
-    nose-cov
+    unittest2
+    pytest
+    pytest-cov
 whitelist_externals =
     sh
     make
     coverage
 commands =
     sh -c 'find . -name "*.pyc" -exec rm -f \{\} +'
+    pip install --force-reinstall pytest mock
     make test-coverage
     coverage xml
 
@@ -68,12 +71,13 @@ deps =
     parameterized
     dict.sorted
     mock
-    nose
+    pytest
 whitelist_externals =
     sh
     make
 commands =
     sh -c 'find . -name "__pycache__" -exec rm -rf \{\} +'
+    pip install --force-reinstall pytest mock
     make test
 
 [flake8]
@@ -89,7 +93,5 @@ max-line-length = 88
 # E203: whitespace before ':'
 ignore = E402,H301,H306,E226,W503,E203
 
-[run]
-omit =
-    tests/*
-    .tox/*
+[pytest]
+addopts = --ignore=tests/_composes