XD-1122 Add mgmtPort option

Adds an option to set the port on which Spring Boot's management
server listens. 

- Added `mgmtPort` as a CommonOption (for both admin/container)
- The management port can also be set via `XD_MGMT_PORT` as an environment
  variable property
- By default, the mangement port uses admin/container server port in
  admin/container servers respectively.