Remove hyphen from rand_name calls in compute tests

data_utils.rand_name() appends randam charactors with a hypen like:

 def rand_name(name=''):
     randbits = str(random.randint(1, 0x7fffffff))
     if name:
         return name + '-' + randbits

So it is not necessary to specify a hypen in caller side.
This patch removes a hypen in compute tests.

Change-Id: Ibed983d75ad9fdbb1f90100863ba0ff1934ab644
diff --git a/tempest/api/compute/base.py b/tempest/api/compute/base.py
index ddfe6de..05bc9f8 100644
--- a/tempest/api/compute/base.py
+++ b/tempest/api/compute/base.py
@@ -247,7 +247,7 @@
         if name is None:
             name = data_utils.rand_name(cls.__name__ + "-securitygroup")
         if description is None:
-            description = data_utils.rand_name('description-')
+            description = data_utils.rand_name('description')
         body = \
             cls.security_groups_client.create_security_group(name,
                                                              description)