Enable py36-py38 testing

- updates tox.ini, also fixing a typo
- enables new jobs, which would at least test ability to install
  package under these versions.
- updates Trove metadata
- replace fake sole-survivor unittest with a bit more practical one

Change-Id: Iae224a19850489ba3563ad5a40d358002dacdb97

.zuul.yaml

@@ -11,6 +11,12 @@
     check:
       jobs:
         - gerritlib-jeepyb-integration
+        - tox-py36
+        - tox-py37
+        - tox-py38
     gate:
       jobs:
         - gerritlib-jeepyb-integration
+        - tox-py36
+        - tox-py37
+        - tox-py38

gerritlib/tests/base.py

@@ -1,5 +1,5 @@
-import testtools
+import unittest
 
 
-class TestCase(testtools.TestCase):
-    "Placeholder wrapper for the testtools.TestCase class."
+class TestCase(unittest.TestCase):
+    "Placeholder wrapper for the TestCase class."

gerritlib/tests/test_gerritlib.py

@@ -19,10 +19,13 @@ test_gerritlib
 Tests for `gerritlib` module.
 """
 
+from gerritlib.gerrit import GerritConnection
 from gerritlib.tests import base
+from paramiko.ssh_exception import NoValidConnectionsError
 
 
 class TestGerritlib(base.TestCase):
 
-    def test_something(self):
-        pass
+    def test_invalid_connection(self):
+        with self.assertRaises(NoValidConnectionsError):
+            GerritConnection(connection_attempts=1, retry_delay=1).connect()

setup.cfg

@@ -20,7 +20,10 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.4
+    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [files]
 packages = gerritlib

test-requirements.txt

@@ -2,4 +2,3 @@ hacking>=0.5.6,<0.11
 sphinx>=1.1.2,<1.2
 python-subunit
 testrepository
-testtools

tox.ini

@@ -1,9 +1,9 @@
 [tox]
 minversion = 1.6
-skipdist = True
-skip_missing_interpreters = true
+skipsdist = True
+skip_missing_interpreters = false
 # https://docs.python.org/devguide/#status-of-python-branches
-envlist = pep8, py27, pypy, py33, py34, py35, py36, py37
+envlist = pep8, py{38,37,36,35,27,py}
 
 [testenv]
 commands = python setup.py test --slowest --testr-args='{posargs}'