bitmaskctl vpn status should allow json output

Like bitmaskctl status --json:

(venv) --- git/bitmask-dev ‹master* ⁇› » bitmaskctl status --json        
WARNING:vext:Could not add extra path: /usr/share/sip
{
  "result": "{\"web\": \"running\", \"keymanager\": \"running\", \"soledad\": \"running\", \"mail\": \"running\", \"vpn\": \"running\", \"backend\": \"default\"}", 
  "error": null
}

bitmaskctl vpn status --json should also allow json output, currently it doesn't:

(venv) --- git/bitmask-dev ‹master* ⁇› » bitmaskctl vpn  status --json   
WARNING:vext:Could not add extra path: /usr/share/sip
status      off
firewall    off
vpn         off
domain      demo.bitmask.net
↑↑↑         5.2 M
↓↓↓         94.7 M