Install prometheus charm on xenial fails

Steps to reproduce:

juju deploy cs:~prometheus-charmers/prometheus-3

Install hook fails:

2016-11-01 12:35:39 INFO juju-log Invoking reactive handler: reactive/prometheus.py:136:write_prometheus_config_yml
2016-11-01 12:35:39 INFO install Traceback (most recent call last):
2016-11-01 12:35:39 INFO install File "/var/lib/juju/agents/unit-prometheus-0/charm/hooks/install", line 19, in <module>
2016-11-01 12:35:39 INFO install main()
2016-11-01 12:35:39 INFO install File "/usr/local/lib/python3.5/dist-packages/charms/reactive/__init__.py", line 78, in main
2016-11-01 12:35:39 INFO install bus.dispatch()
2016-11-01 12:35:39 INFO install File "/usr/local/lib/python3.5/dist-packages/charms/reactive/bus.py", line 434, in dispatch
2016-11-01 12:35:39 INFO install _invoke(other_handlers)
2016-11-01 12:35:39 INFO install File "/usr/local/lib/python3.5/dist-packages/charms/reactive/bus.py", line 417, in _invoke
2016-11-01 12:35:39 INFO install handler.invoke()
2016-11-01 12:35:39 INFO install File "/usr/local/lib/python3.5/dist-packages/charms/reactive/bus.py", line 291, in invoke
2016-11-01 12:35:39 INFO install self._action(*args)
2016-11-01 12:35:39 INFO install File "/var/lib/juju/agents/unit-prometheus-0/charm/reactive/prometheus.py", line 141, in write_prometheus_config_yml
2016-11-01 12:35:39 INFO install ver_major, ver_minor, ver_patch = get_version()
2016-11-01 12:35:39 INFO install File "/var/lib/juju/agents/unit-prometheus-0/charm/reactive/prometheus.py", line 128, in get_version
2016-11-01 12:35:39 INFO install output = subprocess.check_output([get_paths()['promtool'], 'version']).split(b'\n')[0]
2016-11-01 12:35:39 INFO install File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
2016-11-01 12:35:39 INFO install **kwargs).stdout
2016-11-01 12:35:39 INFO install File "/usr/lib/python3.5/subprocess.py", line 693, in run
2016-11-01 12:35:39 INFO install with Popen(*popenargs, **kwargs) as process:
2016-11-01 12:35:39 INFO install File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
2016-11-01 12:35:39 INFO install restore_signals, start_new_session)
2016-11-01 12:35:39 INFO install File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
2016-11-01 12:35:39 INFO install raise child_exception_type(errno_num, err_msg)
2016-11-01 12:35:39 INFO install FileNotFoundError: [Errno 2] No such file or directory: '/snap/bin/prometheus.promtool'
2016-11-01 12:35:39 ERROR juju.worker.uniter.operation runhook.go:107 hook "install" failed: exit status 1
2016-11-01 12:35:39 INFO juju.worker.uniter resolver.go:100 awaiting error resolution for "install" hook