kern-tools: allow meta branch and meta data directory to differ

kern-tools: allow meta branch and meta data directory to differ

From the kern-tools commit:

    tools: allow meta directories that are not the same as the branch name

    With this change it is now possible to have a meta branch with meta data
    in a directory that is not the same name as the branch.

    The changes to three parts of the build are required to discover the name
    of the meta directory by relying on the fact that in a clean/proper build
    the meta directory is the only untracked, top level directory in the build.

    As such, we can restore a checkpoint and then examine the build directory
    to determine the meta directory name .. avoiding any new variables to
    indicate this to the scripts and build system.

(From OE-Core rev: 36823f7aff5c8e28900997c96a97c302947981b0)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>