COOK-2774: Fix freeze when Jenkins is stopped

Chef executes notifications after each resource action, not after all
resource actions are completed.  Previously, if Jenkins was stopped,
these events would occur:

   * runit_service[jenkins] :enable action
   * notify block_until_operational resource
   * runit_service[jenkins] :start action

Because Jenkins was not already running when the
"block_until_operational" resource was executed, Chef would block
forever.

This attempts to fix this by using a separate resource to notify
block_until_operational only after Jenkins is started.

[Fixes [#CHEF-2774](http://tickets.opscode.com/browse/COOK-2774)]