Default to user home directory to read krb5.keytab

This caused issues with zuul jobs, because the user home directories
differ. This also removes hardcoded path from ipa_client.py and
throws a nicer exception if the file is not there.

Change-Id: I6188fe40af1bc5c6549767f45a0acc9f554e5b1e

novajoin_tempest_plugin/config.py

@@ -13,6 +13,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import os
+
 from oslo_config import cfg
 
 service_option = cfg.BoolOpt("novajoin",
@@ -29,7 +31,7 @@ NovajoinGroup = [
                default='vm',
                help='Flavor tag to use in novajoin enrollment tests'),
     cfg.StrOpt('keytab',
-               default='/home/stack/novajoin.keytab',
+               default=os.path.expanduser('~/novajoin.keytab'),
                help='Keytab to connect to IPA as the novajoin user'),
     cfg.StrOpt('tripleo',
                default='True',

novajoin_tempest_plugin/ipa/ipa_client.py

@@ -51,9 +51,12 @@ class IPABase(object):
         except cfg.NoSuchOptError:
             self.keytab = '/etc/novajoin/krb5.keytab'
 
+        with open(self.keytab):
+            pass  # Throw a nicer exception if krb5.keytab does not exist
+
         self.ccache = "MEMORY:" + str(uuid.uuid4())
         os.environ['KRB5CCNAME'] = self.ccache
-        os.environ['KRB5_CLIENT_KTNAME'] = '/home/stack/krb5.keytab'
+        os.environ['KRB5_CLIENT_KTNAME'] = self.keytab
         if self._ipa_client_configured() and not api.isdone('finalize'):
             api.bootstrap(context='novajoin')
             api.finalize()