GUI: simulator: Make simulator item in tools menu return to status screen if sim already active

Signed-off-by: Tim Serong <tserong@suse.com>
GUI: simulator: Make "Run" button restart from current cluster state, not from post-simulate state (bnc#799523)

Signed-off-by: Tim Serong <tserong@suse.com>
GUI: status: Add ability to take nodes on and off maintenance mode

Signed-off-by: Tim Serong <tserong@suse.com>