combo-layer: let user choose where properties get updated
When updating a property (at the moment, only 'last_revision'),
first check whether the user already added it to the main config.
If so, update there even if there is a local config.
This way, 'last_revision' can be shared between developers
as part of the repository while still configuring per-developer
repo paths outside of the git repository in a local config.
An example of a repository which is set up like that is tizen-distro,
with instructions for such a collaborative maintenance found here:
https://review.tizen.org/git/?p=scm/bb/tizen-distro.git;a=blob;f=README;hb=refs/heads/tizen-ivi
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
