Provide ability to suspend and resume the set of servers managed by a specific host controller

In WildFly 10 we introduced the server suspend/resume and graceful shutdown feature. This feature allows the server to complete the active requests normally, without accepting any new requests. A timeout value specifies how long the suspend or shutdown operation waits for active request to complete.

However, there are no specific operations to suspend/resume and shutdown gracefully all servers managed by a specific host controller. These operations can be applied only at server-group or whole domain level. The goal of this issue is to facilitate these tasks to the administrators.

Additionally, the timeout attribute for all of those lifecycle operations will be renamed to suspend-timeout to avoid the confusion of this value with timeout applied to the entire operation. The suspend-timeout attribute has a meaning only for the timeout applied to suspend the servers.