LU-11297 lnet: set gw sensitivity from lnetctl

LU-11297 lnet: set gw sensitivity from lnetctl

Allow an optional parameter from the:
lnetctl route add
command to set the health sensitivity of the gateway
lnetctl route add --net <net> --gateway <gw> --sensitivity <value>

Test-Parameters: forbuildonly
Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: Iee120c78a41b79da6ab6bdf1560f558df89233e2
Reviewed-on: https://review.whamcloud.com/33635
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Tested-by: Jenkins