Server should limit number of workers based on available FD's

Each worker consumes at least 2 FD's for the temp selector, plus one for the active connection. If the FD limit is two low our auto scaling code should account for this and create less workers.

This should also print INFO messages for the auto turned values, and a WARN if the number had to be reduced due to the FD limit.

The FD limit can be accessed through JMX:

ManagementFactory.getOperatingSystemMXBean()
attribute is called "MaxFileDescriptorCount"