eventscript: introduce enum for different event script calls.

eventscript: introduce enum for different event script calls.

Rather than doing strcmp everywhere, pass an explicit enum around.  This
also subtly documents what options are available.  The "options" arg
is now used for extra arguments only.

Unfortunately, gcc complains on empty format strings, so we make
ctdb_event_script() take no varargs, and add ctdb_event_script_args().  We
leave ctdb_event_script_callback() taking varargs, which means callers
have to do "%s", "".

For the moment, we have CTDB_EVENT_UNKNOWN for handling forced scripts
from the ctdb tool.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>