This commit tries to address the possible raceondition that can happen
if a client closes its connection after we have fetched it from the
syncmap before sending the message.
To try to avoid introducing new dead lock conditions, all messages sent
to updateChannel has been moved into a function, which handles the
locking (instead of calling it all over the place)
The same lock is used around the delete/close function.
This commit adds a new field to machine, lastSuccessfulUpdate which
tracks when we last was able to send a proper mapupdate to the node. The
purpose of this is to be able to compare to a "global" last updated time
and determine if we need to send an update map request to a node.
In addition it allows us to create a scheduled check to see if all known
nodes are up to date.
Also, add a helper function to send a message to the update channel of a
machine.
tests for that feature.
Other fixes: clean up a few typos in comments. Fix a bug that caused the
tests to run four times each. Be more consistent in the use of log
rather than fmt to print errors and notices.
