Add support for wait flag in the install script

[msadowski]

Hi!

I run into some cases where I need to pass the wait flag to the roslaunch. This merge request adds a "--wait" option that will change the job.roslaunch_wait that was already implemented.

Please let me know if there is anything else you would like to see changed.

[130s]

+1

@winchesterag and I are discussing adding this --wait to the systemd process. Our particular usecase is to have multiple systemd processes, each of which starts roslaunch, but there's one process that's kind of a central process so other roslaunch processes can depend on the roscore that's started from it. This scenario comes into handy when each systemd process is a Docker or any container where each container is modularized and functions by itself, but can also integrated as part of larger systems.

Though we're not sure the usecase and its design described above is the best optimized way yet, this PR by itself makes sense to me.

[msadowski]

@130s we've been using this modification for close to a year now. In our case the issue we had was a multi-machine setup where we can't control machine boot up time. By adding a wait flag all the machines wait for the 'master computer' to be up and start it's launchfile.

I think this PR should make sense, especially that "roslaunch_wait" was already implemented but not exposed.

[mikepurvis]

LGTM.