combo-layer: ensure init works with split local config

combo-layer: ensure init works with split local config

If the local configuration is already split out, ensure the init action
works properly and does not error in the case that last_revision is not
set. Additionally, if the local configuration is within the repository,
prevent it from being committed and add it to .gitignore.

(From OE-Core rev: de339b0cb201035e27df1128ccf526937b8325ec)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>