add options to configure dnsmasq options in neutron. fixes #709

[JCallicoat]

This adds attributes for neutron dnsmasq options, adds a dnsmasq-nova.conf template with dhcp-option=26,1454, and also allows dhcp-script to be set via attribute.

[rcbjenkins]

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Not automatically merged : JCallicoat is not an approved committer. Please leave pull request open for review and manual merge by a core team member.

[breu]

@JCallicoat it appears that this will set the MTU for instances via DHCP for all network types and not just the ones that are using GRE?

I spoke to @Apsu and we were wondering if you tried allowing ingress ICMP to the instance and allowing pMTUD to set the MTU correctly for the tunneled interface?

[JCallicoat]

@rackerjoe Yeah, setting a dnsmasq config file is at the agent level, so all networks would be effected. I didn't see a way to apply the config per network. I'm not sure if MTU discovery is an option as I don't know the requirements around allowing ICMP. I would think that in at least some cases ICMP would be disallowed by policy. @odyssey4me what do you think? We could make the dhcp-option value a default-nil attribute instead of hard coding it.

[odyssey4me]

@rackerjoe @JCallicoat @Apsu Ingress ICMP should already be allowed by default I think as the DHCP service will sit on the same subnet as the instance and the default policies have a blanket allowance for same subnet traffic.
pMTUD may therefore work, but then where would you apply the MTU restriction.
In the current situation that may actually be what's happening - I'm not versed enough in networking to determine that. All I can say is that in the current deployment there are a lot of dropped packets and retransmissions.
An easy way to resolve it is to ensure that the network where the GRE tunneling is traversing has a higher MTU configured, but the cookbooks can't facilitate that as we don't manage the physical switches or the host ethernet configuration.
Why not make the dhcp-option a default-nil unless the network type is GRE? This puts us in the best of both worlds situation.