Provide ServerEnvironment lookup

The OSGi subsystem requires access to the ServerEnvironment.

Please document (in javadoc) how that can be done.

We currently use a very naive ServerEnvironmentLocator that likely needs improvement.

http://github.com/jbosgi/jboss-as/blob/fe484fab032d134d2fcb5f84bee7575b509cab99/server/src/main/java/org/jboss/as/server/ServerEnvironmentLocator.java