Large-scale deployment tunings for Ironic/Neutron/Nova

This MR adds additional service+DB tunables and configuration tweaks for the large-scale Cascade Lake deployments.

networking-ansible is also disabled and removed from neutron-server image builds, in favor of networking-generic-switch using a Cumulus driver.

added 2 commits

• d36095dd - Ironic enabled and default drivers need tuning to accommodate both drac and...
• 7c7445d2 - Use a custom Nova branch including backported fixes from master against Nova...

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added 1 commit

• 318f2a10 - FIX: Neutron ml2.conf was missing ethsw-dr06-u19 after moving rack back

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added 1 commit

• 95f6194a - Remove extraneous routes: NStor backup and provisioning router reciprocal route

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merged

mentioned in commit 1f89cf10