Replace deprecated method REST keyword

Changes:
    - Keyword RequestsLibrary.Post Request is deprecated.
      Use `POST On Session` instead.

Tested:
    - Ran from sandbox.

Change-Id: I0d4b957b41eeaf61c9f7b3e64ff3d821c066d9f1
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/extended/test_bmc_upload_stability.robot b/extended/test_bmc_upload_stability.robot
index 97fd5e3..cf2c0f0 100755
--- a/extended/test_bmc_upload_stability.robot
+++ b/extended/test_bmc_upload_stability.robot
@@ -54,7 +54,7 @@
 
     ${image_data}=  OperatingSystem.Get Binary File  dummyfile
 
-    # Set up 'openbmc' used in POST request below.
+    # Set up 'redfish' object used in POST request below.
     Initialize OpenBMC
 
     # Create the REST payload headers and data.
@@ -64,7 +64,7 @@
     Set To Dictionary  ${data}  headers  ${headers}
 
     # Upload to BMC and check for HTTP_BAD_REQUEST.
-    ${resp}=  Post Request  openbmc  /upload/image  &{data}
+    ${resp}=  POST On Session  redfish  /upload/image  &{data}
     Should Be Equal As Strings  ${resp.status_code}  ${HTTP_BAD_REQUEST}
 
     ${loop_count}=  Catenate  Ending iteration: ${iteration}