Fixing a bug with multithreading support with the SQLite backend

This change fixes a bug that could occur when accessing the server
with multiple threads or processes. The SQLite backend by default
does not support multithreading. This change updates how the
SQLite backend is instantiated, preventing error generation when
using multiple clients simultaenously. The server unit test suite
has been updated to cover the change.

kmip/services/server/engine.py

@@ -98,7 +98,8 @@ class KmipEngine(object):
 
         self._data_store = sqlalchemy.create_engine(
             'sqlite:////tmp/pykmip.database',
-            echo=False
+            echo=False,
+            connect_args={'check_same_thread': False}
         )
         sqltypes.Base.metadata.create_all(self._data_store)
         self._data_store_session_factory = sqlalchemy.orm.sessionmaker(