Redfish DELETE and get session ID

Changes:
   - Added "DELETE" keyword in client code.
   - Add test to "GET" session Id.
   - Added Teardown methods for clean up test suites.
   - Fixes to accept "None" and user passed session and token.

Resolves  openbmc/openbmc-test-automation#1429

Change-Id: Ibc3a8a58da11068bd1dc77d40bf1648ef1c96c37
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/data/variables.py b/data/variables.py
index 58b0893..900b042 100644
--- a/data/variables.py
+++ b/data/variables.py
@@ -139,6 +139,7 @@
 # Redfish variables.
 REDFISH_BASE_URI = '/redfish/v1/'
 REDFISH_SESSION = REDFISH_BASE_URI + 'SessionService/Sessions'
+REDFISH_SESSION_URI = 'SessionService/Sessions/'
 
 '''
   QEMU HTTPS variable: