…kward compatibility

SBD_WATCHDOG option has been dropped from sbd.sysconfig example.
Re-enabling the support only in the code for backward compatibility.

…tised in sysconfig.sbd

"Default: yes" for SBD_PACEMAKER has always been advertised in
the example sbd.sysconfig. This commit is to ensure that's true again.
It can be disabled by either explicitly setting SBD_PACEMAKER=no in
sysconfig or supplying "-P" option twice like "-P -P".

…-W" and "-w /dev/null" are both supplied

So that it's in conjunction with other descriptions about "Pacemaker
integration" in the man page.