This patch removes unused imports, alse pylint has been configured to
check unused imports.

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

The deprecated has_key method will be removed from dicts in Python 3.

For custom dict-like classes, has_key() is kept on Python 2,
but disabled for Python 3.

Reviewed-By: Tomas Babej <tbabej@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>

Use api.env.basedn instead of anonymously accessing LDAP to get base DN.
Use api.env.basedn instead of searching filesystem for ldapi socket.

https://fedorahosted.org/freeipa/ticket/4953

Reviewed-By: Jan Cholasta <jcholast@redhat.com>
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

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

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

Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>

https://fedorahosted.org/freeipa/ticket/4278

Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>

https://fedorahosted.org/freeipa/ticket/4293

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

These used ipautil.get_ipa_basedn. Convert that to use the new wrappers.

Beef up the error handling in ipaldap to accomodate the errors we catch
in the server discovery.
Add a DatabaseTimeout exception to errors.py.

These were the last uses of ipautil.convert_ldap_error, remove that.

https://fedorahosted.org/freeipa/ticket/3487
https://fedorahosted.org/freeipa/ticket/3446

In addition to removing the module, fix all places where it was imported.

Preparation for: https://fedorahosted.org/freeipa/ticket/3446