Fix to invoke downstream jobs from autorelease jobs

Fix to invoke downstream jobs from autorelease jobs

* Downstream integration test jobs are not getting triggered
due to property file being unavailable in the environment which is requierd
for passing URL bundle link parameter to trigger the
integration-distribution-test job.
* The downstream job is not triggered since the created `variables.props` file
is unavailable to the upstream job and forcing it to fail with (fail-on-missing flag).

Change-Id: I7cac02c39bbbcca48eec1657ee903c64cd60c5a0
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>