Add support to jenkins cmd for jenkins_jobs.ini

Add support to jenkins cmd for jenkins_jobs.ini

Allow the jenkins command to use existing jenkins_jobs.ini for
configuration. By default assume jenkins_jobs.ini's default
configuration 'jenkins'.

This change makes 'server', 'user', and 'password' parameters no
longer required as defaults replace the need for these options.

'server' now defaults to 'jenkins' if jenkins_jobs.ini exists,
otherwise defaults to 'http://localhost:8080' which is the default
Jenkins deploy port.

'user' now defaults to 'admin' which is the Jenkins default admin
user.

'password' has no default and must be set by the user as this
is randomly generated by Jenkins at boot.

Change-Id: Ic7af1eb53e8e9079b845203f44914310616c4bab
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>