Replace nose with unittest and pytest

* Replace raise nose.SkipTest with raise unittest.SkipTest
* Replace nose.tools.assert_equal(a, b) with assert a == b
* Replace nose.tools.raises with pytest.raises
* Convert @raises decorator to pytest.raises() but just for relevant
  lines.
* Remove nose dependency

I left the nose_compat pytest plugin in place. It can be removed in
another request in case it is no longer used.

https://pagure.io/freeipa/issue/7301

Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipatests/test_xmlrpc/test_external_members.py

@@ -21,7 +21,8 @@ Test adding/removing external members (trusted domain objects) to IPA groups.
 These tests are skipped if trust is not established.
 """
 
-import nose
+import unittest
+
 from ipalib import api
 from ipapython.dn import DN
 from ipatests.test_xmlrpc import objectclasses
@@ -53,7 +54,7 @@ class test_external_members(Declarative):
 
         trusts = api.Command['trust_find']()
         if trusts['count'] == 0:
-            raise nose.SkipTest('Trust is not established')
+            raise unittest.SkipTest('Trust is not established')
 
     cleanup_commands = [
         ('group_del', [group_name], {}),