Further clarify the ultimate default server version

* The ultimate default server version should be utilised if the user has
  not defined a jboss server and not set the default server preference.

* Rather than rely on just the hardcoded value, first analyse the runtime
  client plugins installed and choose the latest version to return as this
  ultimate default server value. Only if this fails (should be very rare)
  should the function resort to the hardcoded value.
SPI plugin should be activated on class load

* Since plugin now provides a log and a shared instance plugin, the bundle
  needs to be activated on use of any of its classes.