Change defDemandModeDesired type to bool.

This makes defDemandModeDesired consistent with the DemandMode field of
the bfdSession structure.
Rename bfdMonitorProcessSessionId() to bfdMonitorProcessJsonSessionId().
Make monitor log messages consistent.

All log message from the monitor start with 'MONITOR' or 'MONITOR[<sock>]'.
Python monitor client enhancements.

* Better error handling for session options when subscribing.
* Fixed MonitorMsg instantiation for Unsubscribe (needed sess_opts
  default)
* Allow non-int session opts.
* Changed format of session opts from '<key>:<val>' to '<key>=<val>'.
* Allow splitting session options input with value containing '='.
Add SessionOpts handling to Monitor.

Monitor now extracts SessionOpts values from the Subscribe json
messages.
Stub out 'AuthType' option handling in monitor.

AuthType is not used in the core yet, so this just adds in place holder
comments in the SessionOpts json parser.