Set kernel params in grub config using web UI

* remove hardcoded grub settings
  and set params sended by Nailgun.
* remove code which set parameters
  in /etc/grub.cfg file, this file
  doesn't exist in ubuntu or centos.

Tested on the iso, patches were applied manually.

Depends on: https://review.openstack.org/#/c/90075

Change-Id: I0ad883c087dc39cd4032d739c70466d7aa0098d1
Related-Bug: #1295131
Merge "Set kernel params in grub config using web UI"