fileinstall: run coros in the background if loop already running

* Allow Rose file installation to be called by code which already
  has an event loop running by scheduling coroutines to run in the
  background (i.e. schedule but don't await).
* The calling code can list these tasks using `asyncio.all_tasks()`
  and await them as appropriate.
* Addresses cylc/cylc-rose#274

metomi/rose/job_runner.py

@@ -175,19 +175,28 @@ def run(self, job_manager, *args, concurrency=6):
                 The maximum number of jobs to run concurrently.
 
         """
-        running = []
         loop = asyncio.get_event_loop()
         loop.set_exception_handler(self.job_processor.handle_event)
-        loop.run_until_complete(
-            asyncio.gather(
-                self._run_jobs(running, job_manager, args, concurrency),
-                self._post_process_jobs(running, job_manager, args),
-            )
-        )
+        coro = self._run(job_manager, *args, concurrency=concurrency)
+        try:
+            # event loop is not running (e.g. rose CLI use)
+            loop.run_until_complete(coro)
+        except RuntimeError:
+            # event loop is already running (e.g. cylc CLI use)
+            # WARNING: this starts the file installation running, but it
+            # doesn't wait for it to finish, that's your problem :(
+            loop.create_task(coro)
         dead_jobs = job_manager.get_dead_jobs()
         if dead_jobs:
             raise JobRunnerNotCompletedError(dead_jobs)
 
+    async def _run(self, job_manager, *args, concurrency=6):
+        running = []
+        asyncio.gather(
+            self._run_jobs(running, job_manager, args, concurrency),
+            self._post_process_jobs(running, job_manager, args),
+        )
+
     async def _run_jobs(self, running, job_manager, args, concurrency):
         """Run pending jobs subject to the concurrency limit.