devtool: add finish subcommand

devtool: add finish subcommand

Add a subcommand which will "finish" the work on a recipe. This is
effectively the same as update-recipe followed by reset, except that the
destination layer is required and it will do the right thing depending
on the situation - if the recipe file itself is in the workspace (e.g.
as a result of devtool add), the recipe file and any associated files
will be moved to the destination layer; or if the destination layer is
the one containing the original recipe, the recipe will be overwritten;
otherwise a bbappend will be created to apply the changes. In all cases
the layer path can be loosely specified - it could be a layer name, or
a partial path into a recipe. In the case of upgrades, devtool finish
will also take care of deleting the old recipe.

This avoids the user having to figure out the correct actions when
they're done - they just do "devtool finish recipename layername" and
it saves their work and then removes the recipe from the workspace.

Addresses [YOCTO #8594].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>