Do not always PXE boot Powered off Reserved Servers

[defo89]

Summary

If server OS is installed on disk, we don't want to always PXE boot powered off Reserved servers.

"PXE boot once" should only be performed for Reserved servers that were transitioned from Available to Reserved.

We could signal the need to PXE boot once via annotation or server .Status in the Available state.

[afritzler]

Now about adding a transition condition for a netboot? Once thing we should also do is to a bootType field to the ServerBootConfiguration that will indicate to e.g. the boot-operator when to prepare a net boot. for the bootType=Disk we could transition the ServerBootConfiguration to a Ready state immediately and perform a PowerOn. That way we keep the Server <-> ServerBootConfiguration contract in tact.