Username and Hostname with / break labgrid usage

Hi,

Setup
I'm running labgrid-cooridnator with a self build docker image which uses the master branch
https://github.com/labgrid-project/labgrid/commit/41b297faba60f32e4986678554af32dbff83ce98
I checked this by running git logs on /opt/labgrid within the container.

For connecting to the coordinator I'm using the official image from hub.docker.com:
labgrid/client@sha256:c2808c805d6e14505b5050a1cb493ea1e4ecad81bbde8ce5aaadab0d6cdb8667

Description

If one of the environment variables LG_USERNAME or LG_HOSTNAME contain a /, I'm not able to unlock a reserved place (labgrid-client -p + unlock), nor show the current usage (labgrid-client who).

Procedure

# export LG_USERNAME="user/123"
# export LG_HOSTNAME="host/123"
# labgrid-client places
  p1
# labgrid-client -v places
Place 'p1':
  tags: test=123
  matches:
  acquired: None
  acquired resources:
  created: 2021-08-17 14:54:11.289673
  changed: 2021-09-03 09:15:49.538910
# labgrid-client reserve --shell test=123 > labgrid-token.sh
# source ./labgrid-token.sh
# labgrid-client wait
owner: host/123/user/123
token: SMILMTLDAN
state: allocated
filters:
  main: test=123
allocations:
  main: p1
created: 2021-09-03 09:34:41.672340
timeout: 2021-09-03 09:36:01.812984
# labgrid-client -p + lock
acquired place p1
# labgrid-client -p + show
Place 'p1':
  tags: test=123
  matches:
  acquired: host/123/user/123
  acquired resources:
  created: 2021-08-17 14:54:11.289673
  changed: 2021-09-03 09:37:09.926147
  reservation: SMILMTLDAN

Errors

# labgrid-client who
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/labgrid-0.1.dev1+g41b297f-py3.7.egg/labgrid/remote/client.py", line 1843, in main
    args.func(session)
  File "/usr/local/lib/python3.7/dist-packages/labgrid-0.1.dev1+g41b297f-py3.7.egg/labgrid/remote/client.py", line 272, in print_who
    host, user = place.acquired.split('/')
ValueError: too many values to unpack (expected 2)

# labgrid-client -p + unlock
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/labgrid-0.1.dev1+g41b297f-py3.7.egg/labgrid/remote/client.py", line 1841, in main
    session.loop.run_until_complete(coro)
  File "/usr/lib/python3.7/asyncio/base_events.py", line 584, in run_until_complete
    return future.result()
  File "/usr/local/lib/python3.7/dist-packages/labgrid-0.1.dev1+g41b297f-py3.7.egg/labgrid/remote/client.py", line 629, in release
    _, user = place.acquired.split('/')
ValueError: too many values to unpack (expected 2)

Personal Conclusion

From what I understand, a / should not be allowed in the username or hostname.

Start in labgrid/remote/client.py at print_who and release, the traceback locations for labgrid-client who and unlock. Reproduce with LG_USERNAME and LG_HOSTNAME containing '/', then inspect how the acquired value is formed and consumed. Done means these commands no longer fail for such values, consistent with the issue's proposed username and hostname constraint.