Add workaround for broken git repo polling by Jenkins

Add workaround for broken git repo polling by Jenkins

To save our Jenkins lab resources and Coverity Scan submission quota we
can run the scan if there were recent commits only.

At the moment the following JJB configuration does not work properly for
ONAP repositories:
  triggers:
    - pollscm:
        cron: '@daily'

As a workaround a new job build parameter is introduced -
'max-git-repo-age-hours'. If set to non-zero run the code scan only if
there were no git repository commits last max-git-repo-age-hours hours.
It makes sense to set the value twice the 'cron' interval for the job
(e.g. if 'cron: @daily', then max-git-repo-age-hours=48).

Issue-ID: CIMAN-260
Signed-off-by: Artem Naluzhnyy <A.Naluzhnyy@samsung.com>
Change-Id: I82ce092e9b8bb423e9db8b3958d6cfa3b527b33b