These items conflict when they are provided also in head file
Fixes: #456

* Ensure additional nameserver/search, if defined as vars.
* Don't backup changed dhclient hooks as they are going to be
  executed by dhclient as well, which is not what we want.
* For debian OS family only:
- Rename nodnsupdate hook the resolvconf hook to be sourced always
before it.
- Ensure dhclient restarted via network restart to apply the
nodnsupdate hook.
* For rhel OS family, the fix TBD, it doesn't work the same way.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

This reverts commit 977f82c3.

Rename nodnsupdate hook the resolvconf hook to be sourced always
before it.
Ensure dhclient restarted via network restart to apply the
nodnsupdate hook.
Ensure additional nameserver/search, if defined as vars.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

If resolvconf was installed and then removed, the file
/etc/resolvconf/resolv.conf.d/head remains in the filesystem

- change discovery of 'resolvconf' executable to check if it
  can be located with 'which resolvconf' command or not.

kube-masters without kube-node role will not run
kube-proxy, and therefore can't check if dnsmasq
is running.

Fixes #368

On CoreOS the binaries are not installed in /usr/local/bin.

This fixes cases for use in Vagrant environments.