Ensure compute node IP is in list of DHCP servers

This will work for single network installs, and fixes issue
when live migrating the dhcp rule is wrong.

Change-Id: I407b576d9b58df7f34901f039961fdf0032f46e8
fixup! AZ support for cells

Change-Id: Idbf4208164eb5f01813ec8910cb6cd4a0a553bfa
Support string values for host and service ID

Due to cells prepending the cell routing path this isn't an
int when using cells.

Change-Id: Iaebdc107b8b5628e32fd28a4d859a27a712c47b7