snapcraft snap with an unexisting dir shows a traceback

To reproduce, run:

⟫ snapcraft snap idontexist
Traceback (most recent call last):
  File "/snap/snapcraft/501/bin/snapcraft", line 11, in <module>
    load_entry_point('snapcraft==2.34', 'console_scripts', 'snapcraft')()
  File "/snap/snapcraft/501/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 565, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/snap/snapcraft/501/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2631, in load_entry_point
    return ep.load()
  File "/snap/snapcraft/501/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2291, in load
    return self.resolve()
  File "/snap/snapcraft/501/usr/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2297, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/snapcraft/cli/__main__.py", line 19, in <module>
    run(prog_name='snapcraft')
  File "/snap/snapcraft/501/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/snap/snapcraft/501/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/snapcraft/cli/lifecycle.py", line 132, in snap
    project_options, directory=directory, output=output)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/snapcraft/internal/lifecycle.py", line 345, in snap
    snap = _snap_data_from_dir(prime_dir)
  File "/snap/snapcraft/501/lib/python3.6/site-packages/snapcraft/internal/lifecycle.py", line 330, in _snap_data_from_dir
    with open(os.path.join(directory, 'meta', 'snap.yaml')) as f:
FileNotFoundError: [Errno 2] No such file or directory: '/home/elopio/tmp/idontexist/meta/snap.yaml'

This should show a nicer message.