Changes for Tower virtualenv support

* Break requirements down into ansible and tower reqs
* Generate separate Ansible and Tower virtual environments
* Install appropriate requirements files into each one
* Modify development tools to use these venvs instead of our old
  site-packages
* Modify settings to indicate venv enablement and location of venvs
* Modify tasks to use the proper virtual environment for its purpose

awx/__init__.py

@@ -37,18 +37,6 @@ def find_commands(management_dir):
 def prepare_env():
     # Update the default settings environment variable based on current mode.
     os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'awx.settings.%s' % MODE)
-    # Add local site-packages directory to path.
-    local_site_packages = os.path.join(os.path.dirname(__file__), 'lib',
-                                       'site-packages')
-    site.addsitedir(local_site_packages)
-    try:
-        index = sys.path.index(local_site_packages)
-        sys.path.pop(index)
-        # Work around https://bugs.python.org/issue7744
-        # by moving  local_site_packages to the front of sys.path
-        sys.path.insert(0, local_site_packages)
-    except ValueError:
-        pass
     # Hide DeprecationWarnings when running in production.  Need to first load
     # settings to apply our filter after Django's own warnings filter.
     from django.conf import settings