LU-4318 lbuild: build failed if kernel source in command line

LU-4318 lbuild: build failed if kernel source in command line

For OFED and ZFS builds the function $(find_linux_release) is used.
But it defined in $LBUILD_DIR/lbuild-$DISTRO that is not included
in case of build when kernel source tree was given on the command
line.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: I5f7ae64f560c76e745dc7314465c7fa7d9ec275f
Reviewed-on: http://review.whamcloud.com/8421
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>