support local-rootfs argument to pass local rootfs tarball
support local-rootfs argument to pass local rootfs tarball

This patch adds "--local-rootfs" argument to get a path
of local rootfs tarball. It can be usefull to copy from
local generated rootfs tarball instead of server's one.

Change-Id: I6c856d6c83243a19090a3b78ca018380e4c53ddb
Signed-off-by: Chanho Park <8ec285a53e21b773fd914e03c50e1b6431bc9aa8@samsung.com>

SamsungARTIK/build-artik