ci: build image with timestamp for flux

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

scripts/az_do_set_branch.py

@@ -1,5 +1,6 @@
 """Helper script to get the actual branch name, docker safe"""
 import os
+from time import time
 
 env_pr_branch = "SYSTEM_PULLREQUEST_SOURCEBRANCH"
 default_branch = "BUILD_SOURCEBRANCHNAME"
@@ -9,3 +10,4 @@ if env_pr_branch in os.environ:
     branch_name = os.environ[env_pr_branch].replace("/", "-")
 
 print("##vso[task.setvariable variable=branchName]%s" % branch_name)
+print("##vso[task.setvariable variable=timestamp]%s" % int(time()))