Commands for tracking the mob session

[mpgoodwin-wsa]

I left this comment in the timer github, which should have been here

It would be nice with some command line option for following the current head of the mob.
#> mob join
or
#> mob pull
These would both check out the mob branch. Perhaps the pull version would get to remote head, whereas the mob join just checks out the current branch... Perhaps there is only need for one.

This allows all mob participants to be on the same page when the "baton" passes round the circle. It could also tell the timer who is in, and allow some sort of round robin rather than basing it on the git history. Being able to follow the commits allows all team members to have a recent set of executing tests, minimizing the build time at driver switch.

[mpgoodwin-wsa]

Also we noticed that the mob start command seems to hang, if it is executed twice.