Add support for setting Neutron DHCP agent options.

This patch adds support for setting arbitrary Neutron DHCP agent options.
An example of using it would be to add this to your localrc:

    Q_DHCP_EXTRA_DEFAULT_OPTS=(enable_multihost=True)

Change-Id: I56d267eafa06c52c3867e3396483f5fde3ee5570
VMware: update cinder support for VMware configuration settings

The review https://review.openstack.org/#/c/41600 was update to
have a 'vmware' prefix for all of the VMware cinder settings. These
were previously in a 'vmware' section and now they are in the
'DEFAULT' section.

Change-Id: I8eadfb0f64914d3b0667760aff651415df48f627
Merge "VMware: update cinder support for VMware configuration settings"
Merge "Add support for setting Neutron DHCP agent options."