Return if msiexec.exe will be used and the command to invoke it.

def _get_msiexec(use_msiexec):
    '''
    Return if msiexec.exe will be used and the command to invoke it.
    '''
    if use_msiexec is False:
        return False, ''
    if isinstance(use_msiexec, six.string_types):
        if os.path.isfile(use_msiexec):
            return True, use_msiexec
        else:
            log.warning(
                "msiexec path '%s' not found. Using system registered "
                "msiexec instead", use_msiexec
            )
            use_msiexec = True
    if use_msiexec is True:
        return True, 'msiexec'