varnish/varnishgather — pull request #17 by quiver (2013-10-14 15:27:06+00:00)
Title: error handling for subprocess.Popen OSError

In the probing process, subprocess.Popen raises 'OSError : [Errno 2] No such file or directory'
and exits abruptly in the following case:
- program is not installed(e.g. run dpkg against RedHat flavors)
- program cannot be found in $PATH
- etc.

For such case, just log error message and keep on probing.

# sample output
```
===============================================================================
Command: dummy_command -a
===============================================================================
STDOUT:

STDERR:
[Errno 2] No such file or directory
```