…SBD_PACEMAKER is set

It doesn't necessarily tell whether pacemaker integration is enabled,
since it can be overridden by -P or -PP option.

…-P or -PP option

…ntegration is even intentionally disabled

It doesn't make sense to recommend startup syncing if one doesn't even
want pacemaker integration.

…d while SBD_SYNC_RESOURCE_STARTUP is conflicting

And tell user to fix the configuration by either enabling SBD_PACEMAKER
or explicitly disabling SBD_SYNC_RESOURCE_STARTUP. Otherwise startup of
pacemaker would be hanging forever, since pacemaker only knows about
SBD_SYNC_RESOURCE_STARTUP.