LU-9480 lnet: cleanup lnetctl and cyaml

LU-9480 lnet: cleanup lnetctl and cyaml

lnetctl set commands results in segmentation fault
if no values are provided. This patch makes them
show help if no values are provided to with set commands.

Made general cleanups in the lnetctl code to consolidate
where the help is being printed. Created a function
check_cmd() which checks for the expected number of
arguments and for the -h/--help option and prints
the help string if either scenario is encountered.

fixed the fsm transition in cyaml to allow proper
parsing of empty cyaml documents

Change-Id: Ia081e9304ba2d6baa804e4c8890fb1988d860c1c
Test-Parameters: trivial
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Signed-off-by: Sonia Sharma <sonia.sharma@intel.com>
Reviewed-on: https://review.whamcloud.com/27349
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>