Get ServiceMetadata - not sure if we need to duplicate here
the only concern is if data was already partially read
but so far we read data only while converting to proto and back
or while doing read/write for TaskCompletionEvent
Parse the URL that needs to be notified of the end of the job, along
with the number of retries in case of failure, the amount of time to
wait between retries and proxy settings
Note that this transition method is called directly (and synchronously)
by MRAppMaster's init() method (i.e., no RPC, no thread-switching;
just plain sequential call within AM context), so we can trigger
modifications in AM state from here (at least, if AM is written that
way; MR version is).