Remove pinned vars and set become:true

This patch removes the following pinned vars for test execution:

lxc_container_release:
This variable is set based on the host platform and should not
be fixed to this value in the playbook.

lxc_container_backing_store:
This value is dynamically set based on the host configuration
and 'dir' is the fallback value so it does not need to be set.

global_environment_variables:
This value is an *optional* variable. It was only ever set in
order to test that the functionality to apply the contents of
this variable work.

This patch also sets 'become: true' for the playbook to ensure
that the execution of the container creation/deletion is executed
as the root user.

Change-Id: Id6f35e1b9fef5096c06dffb1900c2d144bc5ece4
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>

destroy_containers.yml

@@ -14,6 +14,7 @@
 # limitations under the License.
 - name: Playbook for destroying test containers
   hosts: all_container
+  become: true
   gather_facts: false
   tasks:
     - name: Destroy a container

test-prepare-containers.yml

@@ -17,13 +17,10 @@
   when: destroy_first | default(True) | bool
 - name: Playbook for creating containers
   hosts: all_containers
+  become: true
   gather_facts: false
   roles:
     - role: "lxc_container_create"
-      lxc_container_release: trusty
-      lxc_container_backing_store: dir
-      global_environment_variables:
-        PATH: "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
   post_tasks:
     - name: Wait for ssh to be available
       local_action: