qa/tasks/cephfs: do no radom.sample(a_dict)

collect the keys instead of filtering a dict,
to address following failure:
```
2020-04-05T12:15:36.275 INFO:tasks.cephfs_test_runner:Traceback (most recent call last):
2020-04-05T12:15:36.275 INFO:tasks.cephfs_test_runner:  File "/home/teuthworker/src/github.com_tchaikov_ceph_wip-qa-py3/qa/tasks/cephfs/test_strays.py", line 29, in test_files_throttle
2020-04-05T12:15:36.275 INFO:tasks.cephfs_test_runner:    self._test_throttling(self.FILES_THROTTLE)
2020-04-05T12:15:36.276 INFO:tasks.cephfs_test_runner:  File "/home/teuthworker/src/github.com_tchaikov_ceph_wip-qa-py3/qa/tasks/cephfs/test_strays.py", line 96, in _test_throttling
2020-04-05T12:15:36.276 INFO:tasks.cephfs_test_runner:    return self._do_test_throttling(throttle_type)
2020-04-05T12:15:36.278 INFO:tasks.cephfs_test_runner:  File "/home/teuthworker/src/github.com_tchaikov_ceph_wip-qa-py3/qa/tasks/cephfs/test_strays.py", line 176, in _do_test_throttling
2020-04-05T12:15:36.278 INFO:tasks.cephfs_test_runner:    mds_max_purge_ops = int(self.fs.get_config("mds_max_purge_ops", 'mds'))
2020-04-05T12:15:36.279 INFO:tasks.cephfs_test_runner:  File "/home/teuthworker/src/github.com_tchaikov_ceph_wip-qa-py3/qa/tasks/cephfs/filesystem.py", line 285, in get_config
2020-04-05T12:15:36.279 INFO:tasks.cephfs_test_runner:    service_id = random.sample(filter(lambda i: self.mds_daemons[i].running(), self.mds_daemons), 1)[0]
2020-04-05T12:15:36.280 INFO:tasks.cephfs_test_runner:  File "/home/teuthworker/src/git.ceph.com_git_teuthology_py3/virtualenv/lib/python3.5/random.py", line 311, in sample
2020-04-05T12:15:36.280 INFO:tasks.cephfs_test_runner:    raise TypeError("Population must be a sequence or set.  For dicts, use list(d).")
2020-04-05T12:15:36.280 INFO:tasks.cephfs_test_runner:TypeError: Population must be a sequence or set.  For dicts, use list(d).
```

Signed-off-by: Kefu Chai <kchai@redhat.com>
(cherry picked from commit 40d0356249193bf4aaa2d38923eef19caa63eb59)

diff --git a/qa/tasks/cephfs/filesystem.py b/qa/tasks/cephfs/filesystem.py
index 24051294ca3e735988e890295aa1d9788707dd72..87396f353227dc8f64cf5f63dc1d9598650f7504 100644 (file)
--- a/qa/tasks/cephfs/filesystem.py
+++ b/qa/tasks/cephfs/filesystem.py
@@ -260,7 +260,8 @@ class MDSCluster(CephCluster):
             return super(MDSCluster, self).get_config(key, service_type)
 
         # Some tests stop MDS daemons, don't send commands to a dead one:
-        service_id = random.sample(filter(lambda i: self.mds_daemons[i].running(), self.mds_daemons), 1)[0]
+        running_daemons = [i for i, mds in self.mds_daemons.items() if mds.running()]
+        service_id = random.sample(running_daemons, 1)[0]
         return self.json_asok(['config', 'get', key], service_type, service_id)[key]
 
     def mds_stop(self, mds_id=None):