Validate URLs using Jenkins env variable

Since we are adding in Jenkins a variable
JIRA_URL, we want to make the logic of this
script so that it picks up its value to look
for related URLs in the commit text rather
than using a static value.

Change-Id: Id6d1df4cfefa0d37f7f74a48d8d5149379ede3eb
Signed-off-by: Jessica Wagantall <jwagantall@linuxfoundation.org>