messages/MWatchNotify: include an error code in the message

Document the fields, while we are here.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit a786d2d0bdb0ac185c83dc7534aa60ccf53b16ff)
osd: include ETIMEDOUT in notify reply on timeout

If a notify operation times out (all watchers to not ACK in time), include
an ETIMEDOUT in the final error message back to the client, so that they
know about it.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 7a2ec05cc8c11e948ff62fe07c00df8692a50b50)
librados: rename watch/notify callback register functions

Make it clear these are for watch OR notify, not just watch.  I was
confused.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 59a9785051cbb59542734902b8f485ddf706f8ad)
librados: prefix msg handler with handle_

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit e4e7a18024910fe3cda89ed2d868ceb26c581168)
librados: refactor watch/notify; return notify error code

Get rid of a level of intermediate classes with confusing names and put
the notify and notify finish logic in a single place so that it is easier
to follow and understand.

Pass the return value from the notify completion message to the caller.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 69612e7519f9fa73d6ac1c6358bfeac33e998774)

Conflicts:
	src/librados/RadosClient.cc