[Buildroot] Adding local file system overlay

[Lars Dunemark]

Hi Buildroot mailinglist!

During development of a new platform I sometimes find it useful to bundle my test builds with my own script/configuration files. 
Example: SSH keys

This is not something that we want to include in default configuration for a board or by any way get in a final build so instead I added a second step to local file system overlay checking a local variable and if it is set us it as a roofs overlay.

Is this something that is of interests for the upstream project?

Example: 
export  LOCAL_ROOTFS_OVERLAY=/local-rootfs-overlay
make

Best regards,
Lars Dunemark