LU-9558 tests: add completion.h header to kinode.c

LU-9558 tests: add completion.h header to kinode.c

When building lustre on a ARM fedora box running a 4.11 kernel
kinode.c failed to build due to the completion.h header missing.
A simple including of this header fixes everything.

Test-Parameters: trivial

Lustre-change: https://review.whamcloud.com/28998
Lustre-commit: 982d660edbcacd528579f25ed2a3ae076a0134f3

Change-Id: I2a193346b214616a6f5dee5049466fb55567e396
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Frank Zago <fzago@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: https://review.whamcloud.com/29567
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>