Allow output configuration from config file.

Allow output configuration from config file.

Parse the config file for [output] sections and check for 'name'
and 'mode' keys. The key strings are compared to what is reported
by weston log. The 'mode' key string can be one of the following:

1) WIDTHxHEIGHT - one that is reported by weston log
2) off - Disables the output
3) preferred - Uses the preferred mode
4) current - Uses the mode currently driving the crtc