Rename wait_for_units param -> wait_for_at_least_units

to make the semantics of `wait_for_units` explicit, which is to wait
for a certain amount of units across all the given applications and
return when those are available, regardless of the state of the other
units (they can be in an error state or whatever just don't care and
return)

Fixes #886

Author: cderici

juju/model.py

@@ -2622,7 +2622,7 @@ async def wait_for_idle(self, apps=None, raise_on_error=True, raise_on_blocked=F
             warnings.warn("wait_for_active is deprecated; use status", DeprecationWarning)
             status = "active"
 
-        _wait_for_units = wait_for_units if wait_for_units is not None else 1
+        _wait_for_units = wait_for_at_least_units if wait_for_at_least_units is not None else 1
 
         timeout = timedelta(seconds=timeout) if timeout is not None else None
         idle_period = timedelta(seconds=idle_period)
@@ -2689,10 +2689,11 @@ def _raise_for_status(entities, status):
                     busy.append(app.name + " (not enough units yet - %s/%s)" %
                                 (len(app.units), _wait_for_units))
                     continue
-                # User wants to see a certain # of units, and we have enough
-                elif wait_for_units and len(units_ready) >= _wait_for_units:
+                # User is waiting for at least a certain # of units, and we have enough
+                elif wait_for_at_least_units and len(units_ready) >= _wait_for_units:
                     # So no need to keep looking, we have the desired number of units ready to go,
-                    # exit the loop. Don't return, though, we might still have some errors to raise
+                    # exit the loop. Don't just return here, though, we might still have some
+                    # errors to raise at the end
                     break
                 for unit in app.units:
                     if unit.machine is not None and unit.machine.status == "error":
@@ -2711,7 +2712,8 @@ def _raise_for_status(entities, status):
                     if not waiting_for_a_particular_status and unit.agent_status == "idle":
                         # We'll be here in two cases:
                         # 1) We're not waiting for a particular status and the agent is "idle"
-                        # 2) We're waiting for a particular status and the workload is in that status
+                        # 2) We're waiting for a particular status and the workload is in that
+                        # status
                         # Either way, the unit is ready, start measuring the time period that
                         # it needs to stay in that state (i.e. idle_period)
                         units_ready.add(unit.name)