Thanks to nexedi/slapos!158 , in a slaprunner we can use slapos command:
```
$ slapos supply https://lab.nexedi.com/nexedi/slapos/raw/1.0.19/software/erp5/software.cfg slaprunner
```
works fine to supply a software to "current" webrunner, but building this software with `slapos node software` fails with:
```
$ slapos node software
2017-10-03 02:46:33 slapos[29536] CRITICAL slapgrid could not write pidfile /opt/slapos/slapgrid-sr.pid
2017-10-03 02:46:33 slapos[29536] ERROR [Errno 13] Permission denied: '/opt/slapos/slapgrid-sr.pid'
Traceback (most recent call last):
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/entry.py", line 300, in run_subcommand
    result = cmd.run(parsed_args)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/command.py", line 50, in run
    return self.take_action(parsed_args)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/slapgrid.py", line 116, in take_action
    setRunning(logger=self.app.log, pidfile=pidfile)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/grid/utils.py", line 155, in setRunning
    write_pid(logger, pidfile)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/grid/utils.py", line 167, in write_pid
    with open(pidfile, 'w') as fout:
IOError: [Errno 13] Permission denied: '/opt/slapos/slapgrid-sr.pid'
```

because slaprunner's web interface also runs software, it's better both `slapos node software` command and the one from slaprunner web interface uses the same pid file so that they do not run in parallel.

This depends on nexedi/slapos.core!29

/reviewed-on nexedi/slapos!235