Replace deprecated import of ABCs from collections

ABCs in collections should be imported from collections.abc and direct
import from collections is deprecated since Python 3.3.

Closes-Bug: #1936667
Change-Id: Ie660b2e4c7dac05822e13b47335620815a7ad1cf
diff --git a/tempest/lib/common/rest_client.py b/tempest/lib/common/rest_client.py
index 573d64e..3f735f5 100644
--- a/tempest/lib/common/rest_client.py
+++ b/tempest/lib/common/rest_client.py
@@ -14,7 +14,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import collections
+from collections import abc
 import email.utils
 import re
 import time
@@ -884,7 +884,7 @@
                                                     resp=resp)
 
     def is_absolute_limit(self, resp, resp_body):
-        if (not isinstance(resp_body, collections.Mapping) or
+        if (not isinstance(resp_body, abc.Mapping) or
                 'retry-after' not in resp):
             return True
         return 'exceed' in resp_body.get('message', 'blabla')