Remove invalid escape sequences

A recent style update to Python 3.6 adds deprecation W605, which
tightens the usage of invalid escape sequences. This patch removes
any instances of invalid escape sequences from the PyKMIP code
base, bringing the library back up to compliance with Python style.

kmip/demos/units/discover_versions.py

@@ -41,7 +41,7 @@ if __name__ == '__main__':
     protocol_versions = list()
     if opts.protocol_versions is not None:
         for version in re.split(',| ', opts.protocol_versions):
-            mm = re.split('\.', version)
+            mm = re.split(r'\.', version)
             protocol_versions.append(ProtocolVersion(int(mm[0]), int(mm[1])))
 
     # Build the client and connect to the server

kmip/services/server/engine.py

@@ -1444,7 +1444,7 @@ class KmipEngine(object):
             else:
                 raise exceptions.InvalidField(
                     "The cryptographic length must correspond to a valid "
-                    "number of bytes (i.e., it must be a multiple of 8)."
+                    "number of bytes; it must be a multiple of 8."
                 )
         else:
             raise exceptions.InvalidField(

kmip/tests/unit/services/server/test_engine.py

@@ -4108,7 +4108,7 @@ class TestKmipEngine(testtools.TestCase):
         self.assertRaisesRegexp(
             exceptions.InvalidField,
             "The cryptographic length must correspond to a valid number of "
-            "bytes \(i.e., it must be a multiple of 8\).",
+            "bytes; it must be a multiple of 8.",
             e._process_derive_key,
             *args
         )