Consolidate the three copies of _doRunCommand() we have now into a single place:

{{{
[kanarip@sara0202 revisor]$ grep -rin "def _doRunCommand" *
revisor/delta/init.py:37: def _doRunCommand(self, command, rundir='/tmp', output=subprocess.PIPE, error=subprocess.STDOUT, inshell=False):
revisor/lm_optical.py:350: def _doRunCommand(self, command, rundir='/tmp', output=subprocess.PIPE, error=subprocess.STDOUT, inshell=False, env=None):
revisor/pungi.py:40: def _doRunCommand(self, command, rundir=None, output=subprocess.PIPE, error=subprocess.STDOUT, inshell=False):
}}}