Make layerupdate collection slightly more reliable and make it easier
to see when updates have actually been captured:
* Split layerbranch into separate layer and branch fields, since there
may not be a layerbranch in existence but we might want to log an
error relating to the branch and layer.
* Show all layerupdates on the update detail page, not just those with
log messages
* Record before and after revisions and show these in the update detail
and layerupdate detail (with links)
* Record return code of update_layer process
* Highlight layer updates with a non-zero return code, errors or
warnings in the output on the update detail page
* Show duration on the layerupdate detail page
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
