Record and log reason for dhcp agent resync

A dhcp resync can be triggered at a number of points, but the actual
resync is done asynchronously by a helper thread.  This means by the
time the resync happens, it's hard to establish what actually caused
it.

There have been a number of problems in production systems that cause
excessive resyncs.  One is a ipv6/dnsmasq issue (rhbz#1077487) and
another is db corruption with duplicate entries [1].  The resync
triggers a whole lot of logs itself, so it becomes very unclear how to
establish any causality.

This change keeps track of what triggered the resync with some helpful
information.  We add a schedule_resync() function to to replace a
explicit set of needs_resync which tracks why it was called.

[1] The logs will contain output like "DBDuplicateEntry
(IntegrityError) (1062, "Duplicate entry
'6d799c6a-7a09-4c1e-bb63-7d30fd052c8a-d3e3ac5b-9962-428a-a9f8-6b2' for
key 'PRIMARY'") ..." in this case

Closes-Bug: #1294445
Change-Id: I9b1c6202f5a6bbad8589a8b64b2a38c9d9edb43b
NSX: fix invalid docstring

Updated the text of docstring.

Change-Id: Ic82fe4719c8b04d01cfb5ebb69411f2f35e7f646
Neutron does not follow the RFC 3442 spec for DHCP

When setting a gateway and additional host routes in neutron subnet, the
gateway is only sent to clients via the router dhcp option, dhcp clients
conforming to rfc3442 will ignore router option if
classless-static-routes are available. This patch ensures setting both
the router option and the classless-static-routes including the gateway

Change-Id: Ia00b9385025020f848872309ae42ddac08528f53
Closes-Bug: #1317935
Remove run-time version checking for openvswitch features

The current method of checking openvswitch and kernel versions for
specific feature support is brittle, distro-specific and unsupportable.

This patch removes the runtime version checks and implements a test
script which allows testing specific neutron features or can test
that all features required by a specific configuration are available.

For example, to test VXLAN support in openvswitch, either:

  neutron-sanity-check --ovs_vxlan

or pass in the deployed configuration files with AGENT/tunnel_types
containing 'vxlan', like:

  neutron-sanity-check --config-file /etc/neutron/plugins/ml2.conf.ini

Deployment tools can then test that the required features exist without
relying on version numbers and without incurring a penalty every time
the agent is started.

Implements: blueprint remove-openvswitch-version-check
DocImpact
Change-Id: I5e822d97b9bece9242ba5ac8901aa0ca4f090cfe
Allow neutron-sanity-check to check OVS patch port support

This patch allows to check OVS patch port support using:

  neutron-sanity-check --ovs_patch

or pass in the deployed configuration files with a non-empty
AGENT/tunnel_types (indeed patch ports are used to interconnect
br-int and br-tun):

  neutron-sanity-check --config-file ml2.conf.ini

DocImpact
Related-Bug: #1285335
Change-Id: Ic7bfabd1f4b85bfa490dd06c70eb5682ee42a681
Merge "NSX: fix invalid docstring"
Merge "Record and log reason for dhcp agent resync"
Merge "Remove run-time version checking for openvswitch features"
Merge "Allow neutron-sanity-check to check OVS patch port support"
Merge "Neutron does not follow the RFC 3442 spec for DHCP"