fix(launcher) workers fail to launch after tunnel

[aminer-looker]

In some environments, the process which establishes the tunnel can
report that it is operational significantly before the tunnel is
actually established. This will cause subsequent calls to create a
worker to fail.

This change waits a short interval after the tunnel process has
reported itself started to allow it to actually finish establishing
the tunnel before attempting to create any workers.

Fixes #42

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[aminer-looker]

My company, Looker Data Services, Inc., has signed the CLA.

[dignifiedquire]

I'm not a big fan of introducing a fixed delay for everyone. Would it be possible to test immediately if the connection is working, and if not do a check every second for 5 seconds or something like that until it becomes available?