Improve the Admin Console loading options

[avpinchuk]

Improve the Administration Console loading options:

• ALWAYS loads the Console at server startup (eager loading)
• DEFAULT loads the Console only after first access to it (on demand loading, used by default)
• Implements NEVER loading option that disable the Admin Console.

Also cleaned up the console-related code.

Usage

Synopsis

asadmin set server.admin-service.property.adminConsoleStartup={default|always|never}

Example

This enforces Admin Console to be loaded at server startup:

asadmin set server.admin-service.property.adminConsoleStartup=always

After setting up the property the domain must be restarted to apply changes.

[OndroMih]

@avpinchuk, this is a nice addition. Wiuld be good to document how to use it (set the loading option via asadmin or admin console) at least here in the PR description. Ideally also in one of the GlassFish guides somewhere.

[avpinchuk]

@OndroMih, I added a description to this PR.

Also I'll think about which reference guide to change.