Don't inject settings for dynamic network

When using Quantum for networking and setting flat_injected to
inject network settings into the guest VM, Nova injects a static
network configuration for networks using DHCP. This change
checks for the existence of a dhcp server and, if found, does not
inject static settings for that network.

Due to limitations of the legacy network info, the fix only
applies when new-style network info is passed to the injection
template function.  The only code still passing in legacy
network info is in libvirt, and there is work ongoing to
remove that dependency.

Fixes bug 1163985
Fixes bug 1112659

Change-Id: I8d3f16bde22e1c6dc0d2432aa263e2b15ae5c93a
Merge "Don't inject settings for dynamic network"