Remove instance['instance_type'] relationship from db api

This removes the entire relationship between an instance and the flavor
it was created from. As such, it removes two tests entirely which
examined the old behavior.

This is one change in a series aimed at removing the use of instance-linked
instance_type objects, in favor of the decoupled type data in
system_metadata. See bug 1140119 for more details.

Change-Id: I8b525a900bf2dc6b193e54aae35fc32248e4cff4
Deprecate CONF.fixed_range, do dynamic setup

Do dynamic fixed_range setup by pulling the networks that should
exist on the host and making the appropriate calls to set up the NAT
entries for each network. This allows for non-contiguous subnets to
be configured in the fixed_ip space and only configures the NAT rules
as they are needed. This also restricts the NAT range to the smallest
range required preventing the NAT from impacting subnets that might
exist on the external network.

DocImpact: For backwards compatibility, Grizzly will still support
the CONF.fixed_range option and if set will perform the default logic
from Folsom and earlier releases. To use the new dynamic fixed_range
setup in Grizzly, set fixed_range='' in your nova.conf. The intention
is to remove the CONF.fixed_range option entirely early in the Havana
cycle and use the dynamic fixed_range setup from Havana going
forward.

Change-Id: I4ec111079f7a1d253190e6a6008048f992a53f68
Fixes: bug #741626 bug #966175
Merge "Deprecate CONF.fixed_range, do dynamic setup"
Merge "Remove instance['instance_type'] relationship from db api"