Automatic merge from submit-queue (batch tested with PRs 61871, 61890, 61786). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Specify DHCP domain for hostname

**What this PR does / why we need it**:

In 9a8c6db4, we looked at the hostname
in the metadata service and used '.' as the delimiter to chop off the
dhcp_domain (specified in nova.conf). However administrators need to
better control the dhcp domain better as there may be a '.' in the host
name itself. So let's introduce a config option that we can use and
default it to what nova uses when dhcp_domain is not specified which is
"novalocal"


**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
new dhcp-domain parameter to be used for figuring out the hostname of a node
```