replace hardcoded references to AdminServer with global class-attribute.

[makker-nl]

• Added global class attribute ADMIN_SERVER_NAME defaulted to 'AdminServer'. This makes it available everywhere, without having to cd() to the root.
• In createBaseDomain() update ADMIN_SERVER_NAME to adminName, after setting the AdminServer.Name.
• Checked every occurrence of hardcoded 'AdminServer' and replaced it with self.ADMIN_SERVER_NAME
• In enable_admin_channel() adminserver name was determined in the correct way (by getting it from the adminServerName property on the root. However, I replaced that with the self.ADMIN_SERVER_NAME, to have it similar to the other references.

[makker-nl]

Nice! Thank you very much.