Optimize Rally imports to reduce start time

* Load plugins only if they are required
  This reduce a lot starting time of Rally and will
  allows us to do online bash completition

  As well it cleans up project structure a lot, e.g.
  all plugins are loaded in single place +
  we don't have strange code in cliutils

* Replace rally.ui.utils to not import mako
  and remove all code on module level

* Make Rally DB lazy inited

* Import plugins during test run

----

The best way to test changes in start up time is to
compare "time rally version" e.g.:

before this patch:
$ time rally version
0.0.5
real	0m0.397s
user	0m0.299s
sys	0m0.089s

after this patch:
0.0.5

real	0m0.281s
user	0m0.200s
sys	0m0.077s

Change-Id: Ibec2e6da66a1304730e801de307df7a1da68d51f

rally/plugins/__init__.py

@@ -0,0 +1,43 @@
+# Copyright 2015: Mirantis Inc.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import os
+
+import decorator
+
+from rally.common.plugin import discover
+
+
+PLUGINS_LOADED = False
+
+
+def load():
+    global PLUGINS_LOADED
+
+    if not PLUGINS_LOADED:
+        discover.import_modules_from_package("rally.deployment.engines")
+        discover.import_modules_from_package("rally.deployment.serverprovider")
+        discover.import_modules_from_package("rally.plugins")
+
+        discover.load_plugins("/opt/rally/plugins/")
+        discover.load_plugins(os.path.expanduser("~/.rally/plugins/"))
+
+    PLUGINS_LOADED = True
+
+
+@decorator.decorator
+def ensure_plugins_are_loaded(f, *args, **kwargs):
+    load()
+    return f(*args, **kwargs)

tests/unit/test.py

@@ -21,6 +21,7 @@ from oslotest import base
 from oslotest import mockpatch
 
 from rally import db
+from rally import plugins
 from tests.unit import fakes
 
 
@@ -41,6 +42,7 @@ class TestCase(base.BaseTestCase):
     def setUp(self):
         super(TestCase, self).setUp()
         self.addCleanup(mock.patch.stopall)
+        plugins.load()
 
     def _test_atomic_action_timer(self, atomic_actions, name):
         action_duration = atomic_actions.get(name)