Use tempest.lib code in tempest

Now that tempest_lib code is copied back into tempest, stop using
tempest_lib in tempest, and start using the copied code.

Remove the dependency to tempest_lib from requirements, and drop
the script to use tempest_lib in tempest. Add os-testr to the
test-requirements.

Partially implements bp tempest-lib-reintegration

Change-Id: I21ab5fe6349f72c98ac9f960a29bf62e813f8b1b
diff --git a/tempest/test.py b/tempest/test.py
index a93903e..45b818f 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -27,7 +27,6 @@
 from oslo_utils import importutils
 import six
 from six.moves import urllib
-from tempest_lib import decorators
 import testscenarios
 import testtools
 
@@ -39,6 +38,7 @@
 import tempest.common.validation_resources as vresources
 from tempest import config
 from tempest import exceptions
+from tempest.lib import decorators
 
 LOG = logging.getLogger(__name__)