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>

The 'as' syntax works from Python 2 on, and Python 3 will
drop the "comma" syntax.

Reviewed-By: Tomas Babej <tbabej@redhat.com>

https://fedorahosted.org/freeipa/ticket/3090

Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>

Pytest will consider each Declarative test individually, running
setup/teardown for each one.
Move the setup and teardown to the class level.

https://fedorahosted.org/freeipa/ticket/4610

Reviewed-By: Tomas Babej <tbabej@redhat.com>

The setUp/dearDown names are used in the unittest module, but there is no reason
to use them in non-`unittest` test cases.
Nose supports both styles (but mixing them can cause trouble when
calling super()'s methods).
Pytest only supports the new ones.

https://fedorahosted.org/freeipa/ticket/4610

Reviewed-By: Tomas Babej <tbabej@redhat.com>

https://fedorahosted.org/freeipa/ticket/4052

Reviewed-By: Petr Viktorin <pviktori@redhat.com>

Using the in-tree binary makes testing outside the source tree
impossible.
Use ipa-getkeytab from $PATH, and add the directory to $PATH when
running the in-tree tests.

Part of the work for https://fedorahosted.org/freeipa/ticket/3654

Reviewed-By: Martin Kosek <mkosek@redhat.com>

Rename the 'tests' directory to 'ipa-tests', and create an ipa-tests RPM
containing the test suite

Part of the work for: https://fedorahosted.org/freeipa/ticket/3654