Import from tempest stable manager

This patch removes the copy of tempest scenario manager
and directly imports the manager from tempest which has been
marked stable in tempest 27.0.0 release.

Change-Id: I403d5bc2eef464e6071e466aeab8e040b9055568
diff --git a/requirements.txt b/requirements.txt
index 6706885..40ef3a4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,4 +6,4 @@
 oslo.config>=5.1.0 # Apache-2.0
 six>=1.10.0 # MIT
 oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
-tempest>=17.1.0 # Apache-2.0
+tempest>=27.0.0 # Apache-2.0