LU-9934 build: support for gcc7

LU-9934 build: support for gcc7

Supress few false warnings with a compiler option when
building the lustre kernel modules. A few other fixes
to make lustre buildable on Fedora.

Change-Id: If14d226e5d92ae9ce54e216d032df94d9398654e
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: https://review.whamcloud.com/28810
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>