LU-1808 build: Lustre build does not support FC15.

Change lbuild to support for FC15 and calm down warning message.

Signed-off-by: yang sheng <ys@whamcloud.com>
Change-Id: I365f708f82c01b0f72aeffa3c09e46800ca770d5
Reviewed-on: http://review.whamcloud.com/3849


Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Reviewed-by: Chris Gearing <chris.gearing@intel.com>
Reviewed-by: Brian J. Murrell <brian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>