Use cluster kernel_params if node kernel_params is not set

Current UX messes with kernel_params setter logic

If kernel_params is modified after node is added to cluster -
kernel_params on node wont be changed

After this fix cluster kernel params will be sended to
orchestrator if no specific params provided for node

Change-Id: Ic03aaf92942d9e7f3c568460aaa0bd5d83cdb51b
Closes-Bug: #1341486
Merge "Use cluster kernel_params if node kernel_params is not set"