lsfd: introduce -p/--pid option, pids filter working in the early stage

lsfd: introduce -p/--pid option, pids filter working in the early stage

    $ time sudo ./lsfd -Q '(PID == 1) or (PID == 2)' > /dev/null

    real	0m0.508s
    user	0m0.230s
    sys	0m0.267s

    $ time sudo ./lsfd -p 1,2 > /dev/null

    real	0m0.088s
    user	0m0.036s
    sys	0m0.033s

    $ [ $(./lsfd -p 1,2) = $(./lsfd -Q '(PID == 1) or (PID == 2)') ]
    $ echo $?
    0

Signed-off-by: Masatake YAMATO <yamato@redhat.com>