node-proxy: add a lock mechanism

node-proxy: add a lock mechanism

The loop in the reporter agent has to wait that the data are all
collected before checking and pushing them to the ceph-mgr (if needed).
The idea is to use the lock mechanism offered by the threading module
from python.

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>
(cherry picked from commit fe03bf3676ee2b351a0155491bc5eb4bb7b3d1a3)