Refactor: libpacemaker: Default to sync dispatch in pcmk_cluster_queries

If message_timeout_ms == 0 for various functions in
pcmk_cluster_queries.c, default to using sync dispatch instead of
starting a mainloop with timeout 30s that behaves basically like sync
dispatch.

This makes it easier to reason about calling these functions when the
caller may have its own mainloop.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>