lslocks: detect blocked locks, fix /proc/locks parser

$ flock foo -c "sleep 100" & flock foo -c "sleep 100"

old version:
  $ lslocks
  lslocks: failed to parse pid: 'WRITE'

new version:

COMMAND           PID  TYPE  SIZE MODE   M      START        END PATH
[...]
flock            1318 FLOCK    0B WRITE* 0          0          0 /home/projects/
flock            1319 FLOCK    0B WRITE  0          0          0 /home/projects/

 The asterisk (e.g. WRITE*) is used for blocked processes.

Reported-by: Mantas Mikulenas <grawity@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>