Update global-requirement for tempest-lib

The latest tempest-lib contains network service clients.
This patch bumps the version for the latest to use these clients.

Change-Id: Ie841385345860d6426ebbdff015dde9556667b36
Depends-on: I70a69e3909e52476dd0485742302bf4737618fc3
diff --git a/requirements.txt b/requirements.txt
index 469b294..031b600 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -21,6 +21,6 @@
 iso8601>=0.1.9
 fixtures>=1.3.1
 testscenarios>=0.4
-tempest-lib>=0.12.0
+tempest-lib>=0.13.0
 PyYAML>=3.1.0
 stevedore>=1.5.0 # Apache-2.0