Remove "node" parameter from methods handling power state in docs
Remove "node" parameter from methods handling power state in docs

This patch fixes the doc about methods handling power state
to remove the parameter "node".
* validate
* get_power_state
* set_power_state
* reboot

Change-Id: I5c0425e1502f304b62566aa1e63823214888ef66
Partial-Bug: #1312632

supermari0/ironic,openstack/ironic,debayanray/ironic_backup,naterh/ironic,openstack/ironic,hpproliant/ironic,rackerlabs/ironic,rdo-management/ironic,bacaldwell/ironic,devananda/ironic,NaohiroTamura/ironic,dims/ironic,NaohiroTamura/ironic,pshchelo/ironic,faizan-barmawer/openstack_ironic,SauloAislan/ironic,ramineni/myironic,bacaldwell/ironic,Tan0/ironic,froyobin/ironic,dims/ironic,ionutbalutoiu/ironic,redhat-openstack/ironic,pshchelo/ironic,naototty/vagrant-lxc-ironic,naototty/vagrant-lxc-ironic,SauloAislan/ironic,ionutbalutoiu/ironic,Tehsmash/ironic