Fix version number extraction for all cases

When the jobs upgrade to a later version of Java passing
"openjdk11" or "openjdk10" the string substitution would only
return the last char which would potentially fail to pick up
the correct version of Java.

This change fixes this issue to handle all cases.

Change-Id: If81100bbdd116ee071c3ecdeeadc0a3016fa2a15
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>