Fix ssh await and fix integration test

Author: hpidcock

juju/unit.py

@@ -222,7 +222,7 @@ def set_meter_status(self):
         """
         raise NotImplementedError()
 
-    def ssh(
+    async def ssh(
             self, command, user=None, proxy=False, ssh_opts=None):
         """Execute a command over SSH on this unit.
 
@@ -232,7 +232,7 @@ def ssh(
         :param str ssh_opts: Additional options to the `ssh` command
 
         """
-        self.machine.ssh(command, user, proxy, ssh_opts)
+        return await self.machine.ssh(command, user, proxy, ssh_opts)
 
     def status_history(self, num=20, utc=False):
         """Get status history for this unit.

tests/integration/test_errors.py

@@ -18,7 +18,7 @@ async def test_juju_api_error(event_loop):
 
     async with base.CleanModel() as model:
         with pytest.raises(JujuAPIError):
-            await model.add_machine(constraints={'mem': 'foo'})
+            await model.add_machine(constraints={'mem': -50})
 
 
 @base.bootstrapped