[multipathd]

[multipathd]

Complete the uevent framework.

The missing bit was the devmap add/remove events handling. Now that it
is in place, get rid of wait_thr altogether : kill the waiters vector,
the "lease" thing.

Helpers added in the process :

o libmultipath/devmapper.c:dm_mapname()
o libmultipath/structs.c:find_mp_by_minor()

Worth noting, devmap remove uevents don't get reliably delivered.
If someone have an explanation I'm interested.