Use default connection check intervals/timeouts in the EFM plugin

[aaron-congo]

• previously, the interval/timeout values could be set to 0 or Long.MAX_VALUE. This PR changes these values to specified defaults when a user-supplied setting is not available
• also changed various EFM variables to thread-safe variants. These variables are shared between the main thread and the monitor thread

[davecramer]

So I'm looking at the title of this and trying to determine how it could be set to MAX_VALUE ?

[congoamz]

So I'm looking at the title of this and trying to determine how it could be set to MAX_VALUE ?

There were a couple spots where this.connectionCheckInvervalMillis was being set to the return value of findShortestIntervalMillis in the MonitorImpl file. The original implementation of this function returned MAX_VALUE if there were no contexts in the MonitorImpl class. The fix for this specific problem is in the MonitorImpl changes in this PR