Allow sub-second intervals in broker configuration settings that take a value in seconds.
There was an ad-hock change to allow link-maintenance-interval to be specified as a floating point value.
Implement a more consistent approach allowing intervals to be expressed as any of
10 - value in seconds, backward compatible.
10s - value in seconds
10ms - value in milliseconds
10us - value in microseconds
10ns - value in nanoseconds