contint: update Jenkins command line

Debian package has introduced:

+JAVA_ARGS="-Djava.awt.headless=true"  # Allow graphs etc. to work even
when an X server is present

Keep our version in sync.

Change-Id: I4ebea4a51d0981d530f54734ead88d3e0778cf7e
Merge "contint: update Jenkins command line" into production