Move import to import block again

Since tempest.stress.driver doesn't use the admin manager in a static
variable anylonger we can move the import back to the block.

Change-Id: I4f720e4528f155f57ec0b3ce44e762d3290de55d
diff --git a/tempest/stress/run_stress.py b/tempest/stress/run_stress.py
index e5cc281..067b994 100755
--- a/tempest/stress/run_stress.py
+++ b/tempest/stress/run_stress.py
@@ -24,6 +24,7 @@
 from unittest import loader
 
 from tempest.openstack.common import log as logging
+from tempest.stress import driver
 
 LOG = logging.getLogger(__name__)
 
@@ -68,8 +69,6 @@
 
 
 def main(ns):
-    # NOTE(mkoderer): moved import to make "-h" possible without OpenStack
-    from tempest.stress import driver
     result = 0
     if not ns.all:
         tests = json.load(open(ns.tests, 'r'))