Port from python-krbV to python-gssapi

python-krbV library is deprecated and doesn't work with python 3. Replacing all
it's usages with python-gssapi.

- Removed Backend.krb and KRB5_CCache classes
  They were wrappers around krbV classes that cannot really work without them
- Added few utility functions for querying GSSAPI credentials
  in krb_utils module. They provide replacements for KRB5_CCache.
- Merged two kinit_keytab functions
- Changed ldap plugin connection defaults to match ipaldap
- Unified getting default realm
  Using api.env.realm instead of krbV call

Reviewed-By: Jan Cholasta <jcholast@redhat.com>
Reviewed-By: Robbie Harwood <rharwood@redhat.com>
Reviewed-By: Simo Sorce <ssorce@redhat.com>

ipatests/test_cmdline/cmdline.py

@@ -22,7 +22,6 @@ Base class for all cmdline tests
 """
 
 import nose
-import krbV
 import distutils.spawn
 import os
 
@@ -33,11 +32,9 @@ from ipatests.test_xmlrpc.xmlrpc_test import XMLRPC_test
 from ipaserver.plugins.ldap2 import ldap2
 
 # See if our LDAP server is up and we can talk to it over GSSAPI
-ccache = krbV.default_context().default_ccache()
-
 try:
     conn = ldap2(api)
-    conn.connect(ccache=ccache)
+    conn.connect()
     conn.disconnect()
     server_available = True
 except errors.DatabaseError: