Adds 'service-num-retries' config option.

Supports services that take unpredictably long time to start up by allowing a
larger value to be specified in the Beaker config.

Additionally, this could be used to change the timeout constraint on a service
during acceptance testing to test against start up times that are too large, or
even just to establish a baseline. This would require running on a host with
very well-known capabilities and load characteristics at any given time.

Signed-off-by: Wayne <wayne@puppetlabs.com>