Add branch checkout option in DMTF tools

Change-Id: Iec22ed736709ce972cc6e36810ac859e71e04e96
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/lib/dmtf_tools_utils.robot b/lib/dmtf_tools_utils.robot
index 2bc2d3d..419dc45 100644
--- a/lib/dmtf_tools_utils.robot
+++ b/lib/dmtf_tools_utils.robot
@@ -8,6 +8,7 @@
 
 # ignore_err controls Shell Cmd behavior.
 ${ignore_err}     ${0}
+${stable_branch}  master
 
 *** Keywords ***
 
@@ -19,7 +20,7 @@
     # rsv_dir_path    Directory path for rsv tool (e.g. "Redfish-Service-Validator").
     # rsv_github_url  Github URL link(e.g "https://github.com/DMTF/Redfish-Service-Validator").
 
-    ${rc}  ${output}=  Shell Cmd  rm -rf ${rsv_dir_path} ; git clone ${rsv_github_url} ${rsv_dir_path}
+    ${rc}  ${output}=  Shell Cmd  rm -rf ${rsv_dir_path} ; git clone --branch ${stable_branch} ${rsv_github_url} ${rsv_dir_path}
 
 
 Run DMTF Tool