Use opentrons dynamic labware for intermittently available hardware like the loader

[saNistoRoboto]

No description provided.

[pbeaucage]

see discussion here: Opentrons/opentrons#7619

this is an intensive fix.

[pbeaucage]

One easy way to implement this would be to add 3 endpoints to OT2Driver.py:

@Driver.unqueued()
def mark_loader_safe(self, whatever):
     self.loader_transfer_is_safe = True
@Driver.unqueued()
def mark_loader_unsafe(self, whatever):
    self.loader_transfer_is_safe = False

def pre_execute():
   if (loader_loc) in task.source or loader_loc in task.dest:
        wait_started = datetime.datetime.now()
        while not self.loader_transfer_is_safe:
            time.sleep(1)
            warnings.warn('attempting transfer to / from loader but that is not safe.  I'm going to wait till it is safe')
            if ( (datetime.datetime.now() - wait_started)>loader_safety_timeout):
                raise AppropriateExceptionTypeHere

And loader._arm_down sends an API call to mark_loader_unsafe and v/v for loader._arm_up

@martintb is this going to work with how flask servers are multithreaded?

[pbeaucage]

Also secrets for the unqueued endpoints so that pen testing robots like ansible don't trigger them...

[pbeaucage]

This pre_execute goes well with #35 also.

[martintb]

Also we should be able to disable the loader from needing to talk to the robot but, in normal operations, it should yell if it can't talk to the OT2 and probably not complete the arm motion.