Ensure that venv is used

This is to ensure that the charm doesn't trample on the system packages
for the things that it needs to install, and that it will cooperate with
another reactive charm, especially as it is a subordinate.

Also fix some PEP8 E722 errors as that seems to have been added to the
pep8 standard set.

Change-Id: I9efb78c6f738db2284677dbde85f9e2a3ed0a6fe

.gitignore

@@ -5,3 +5,4 @@ interfaces
 trusty
 .testrepository
 __pycache__
+.stestr

src/layer.yaml

@@ -1,3 +1,6 @@
 includes: ['layer:openstack', 'interface:barbican-hsm']
 repo: https://github.com/openstack/charm-barbican-softhsm
-
+options:
+  basic:
+    use_venv: true
+    include_system_packages: true

unit_tests/test_lib_barbican_softhsm.py

@@ -47,8 +47,8 @@ class TestSoftHSM(test_utils.PatchHelper):
         # test with no file (patch open so that it raises an error)
         mock_open = mock.MagicMock(return_value=mock.sentinel.file_handle)
         with mock.patch('builtins.open', mock_open):
-            def raise_exception():
-                raise Exception("Supposed to break")
+            def raise_exception(*args):
+                raise OSError("Supposed to break")
             mock_open.side_effect = raise_exception
             pin, so_pin = softhsm.read_pins_from_store()
             self.assertEqual(pin, None)