qa - vault failure on xenial

Analyzer: https://jenkaas.s3.amazonaws.com/954f9e54-6361-41e4-a16b-d13df1ecb640/index.html
Crashdump: https://jenkaas.s3.amazonaws.com/954f9e54-6361-41e4-a16b-d13df1ecb640/artifacts.tar.gz

Traceback:

Traceback (most recent call last):
File "/var/lib/juju/agents/unit-kubernetes-master-1/.venv/lib/python3.5/site-packages/charms/reactive/__init__.py", line 74, in main
bus.dispatch(restricted=restricted_mode)
File "/var/lib/juju/agents/unit-kubernetes-master-1/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 390, in dispatch
_invoke(other_handlers)
File "/var/lib/juju/agents/unit-kubernetes-master-1/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 359, in _invoke
handler.invoke()
File "/var/lib/juju/agents/unit-kubernetes-master-1/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 181, in invoke
self._action(*args)
File "/var/lib/juju/agents/unit-kubernetes-master-1/charm/reactive/kubernetes_master.py", line 2631, in create_secure_storage
vaultlocker.create_encrypted_loop_mount(encryption_conf_dir)
File "lib/charms/layer/vaultlocker.py", line 173, in create_encrypted_loop_mount
check_call(['losetup', '-f', backing_file])
File "/usr/lib/python3.5/subprocess.py", line 576, in check_call
retcode = call(*popenargs, **kwargs)
File "lib/charms/layer/status.py", line 186, in _patched_call
return _orig_call(cmd, *args, **kwargs)
File "/usr/lib/python3.5/subprocess.py", line 557, in call
with Popen(*popenargs, **kwargs) as p:
File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.5/subprocess.py", line 1490, in _execute_child
restore_signals, start_new_session, preexec_fn)
TypeError: Can't convert 'PosixPath' object to str implicitly
Traceback (most recent call last):
File "/var/lib/juju/agents/unit-kubernetes-master-0/.venv/lib/python3.5/site-packages/charms/reactive/__init__.py", line 74, in main
bus.dispatch(restricted=restricted_mode)
File "/var/lib/juju/agents/unit-kubernetes-master-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 390, in dispatch
_invoke(other_handlers)
File "/var/lib/juju/agents/unit-kubernetes-master-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 359, in _invoke
handler.invoke()
File "/var/lib/juju/agents/unit-kubernetes-master-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 181, in invoke
self._action(*args)
File "/var/lib/juju/agents/unit-kubernetes-master-0/charm/reactive/kubernetes_master.py", line 2631, in create_secure_storage
vaultlocker.create_encrypted_loop_mount(encryption_conf_dir)
File "lib/charms/layer/vaultlocker.py", line 173, in create_encrypted_loop_mount
check_call(['losetup', '-f', backing_file])
File "/usr/lib/python3.5/subprocess.py", line 576, in check_call
retcode = call(*popenargs, **kwargs)
File "lib/charms/layer/status.py", line 186, in _patched_call
return _orig_call(cmd, *args, **kwargs)
File "/usr/lib/python3.5/subprocess.py", line 557, in call
with Popen(*popenargs, **kwargs) as p:
File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.5/subprocess.py", line 1490, in _execute_child
restore_signals, start_new_session, preexec_fn)
TypeError: Can't convert 'PosixPath' object to str implicitly