Add ignore statement to log out for BMC manager suite

Boot plugin deletes the sessions, however not all in the suite uses
boot. Ignore the logout failure if there is any

Change-Id: I2cffe2604a3809f72058267a754be15da420ab02
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/redfish/managers/test_managers_bmc.robot b/redfish/managers/test_managers_bmc.robot
index a15ed50..72058d1 100644
--- a/redfish/managers/test_managers_bmc.robot
+++ b/redfish/managers/test_managers_bmc.robot
@@ -156,4 +156,4 @@
     [Documentation]  Do the post test teardown.
 
     FFDC On Test Case Fail
-    redfish.Logout
+    Run Keyword And Ignore Error  redfish.Logout