unitdata.KvStore() is not properly mocked out in the unit tests leading to race failures

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Failed 1 tests - output below:
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unit_tests.test_ceph_radosgw_context.HAProxyContextTests.test_ctxt
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Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/home/zuul/src/opendev.org/openstack/charm-ceph-radosgw/.tox/py36/lib/python3.6/site-packages/mock/mock.py", line 1346, in patched
    return func(*newargs, **newkeywargs)

      File "/home/zuul/src/opendev.org/openstack/charm-ceph-radosgw/unit_tests/test_ceph_radosgw_context.py", line 66, in test_ctxt
    self.assertEqual(expect, haproxy_context())

      File "hooks/ceph_radosgw_context.py", line 59, in __call__
    ctxt = super(HAProxyContext, self).__call__()

      File "hooks/charmhelpers/contrib/openstack/context.py", line 953, in __call__
    db = kv()

      File "hooks/charmhelpers/core/unitdata.py", line 524, in kv
    _KV = Storage()

      File "hooks/charmhelpers/core/unitdata.py", line 189, in __init__
    self._init()

      File "hooks/charmhelpers/core/unitdata.py", line 389, in _init
    )''')

    sqlite3.OperationalError: database is locked