'Return the path of the shell command named C{commandName}, looking at
common locations.'

def getCommand(self, commandName):

    binLoc = FilePath('/bin').child(commandName)
    usrbinLoc = FilePath('/usr/bin').child(commandName)
    if binLoc.exists():
        return binLoc._asBytesPath()
    elif usrbinLoc.exists():
        return usrbinLoc._asBytesPath()
    else:
        raise RuntimeError(('%s    not    found    in    /bin    or    /usr/bin' % (commandName,)))
