Update vlan checking: (#171)

## Description

<!--- Please describe what this PR is going to change -->
Check if `vlan_id=` exists and if it has a value. This allows for an
empty `vlan_id=` value.

## Why is this needed

<!--- Link to issue you have raised -->

Fixes: #

## How Has This Been Tested?
<!--- Please describe in detail how you tested your changes. -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->


## How are existing users impacted? What migration steps/scripts do we
need?

<!--- Fixes a bug, unblocks installation, removes a component of the
stack etc -->
<!--- Requires a DB migration script, etc. -->


## Checklist:

I have:

- [ ] updated the documentation and/or roadmap (if required)
- [ ] added unit or e2e tests
- [ ] provided instructions on how to upgrade

Author: jacobweinstock

files/dhcp.sh

@@ -11,7 +11,8 @@ run_dhcp_client() {
 	one_shot="$1"
 	al="eth*"
 
-	if grep "vlan_id" /proc/cmdline; then
+	vlan_id=$(sed -n 's/.*vlan_id=\([0-9]*\).*/\1/p' /proc/cmdline)
+	if [ -n "$vlan_id" ]; then
 		al="eth*.*"
 	fi