Allow configuring the wsgi pool size

Expose the number of greenthreads in wsgi pool to configuration. This
allows to put a limit to the number of resources like memcache
connections used.

DocImpact
Change-Id: I6e53d6e12661ed2f42a6b543891b13eec0c8300c
Add extra_resources field to compute_nodes table

The compute_nodes table has informtion about allocation and
availability of a predefined set of resources (e.g. memory,
disk, vcpu). The extra_resources field will contain a json
string of arbirtrary information describing an extensible set
of resources that will be tracked by resource tracker plug-ins.

This differs from other fields containing json strings that have
been added recently, including pci_stats and metrics. In particular,
pci_stats is used for information about pci devices, whereas metrics
contains continuously monitored usage data and is updated at different
times to extra_resources and according to a different trigger.
Accordingly, it makes sense to seperate these into different fields.

This is part of: blueprint extensible-resource-tracking

Change-Id: I75e339c2a2827875078c937e57c37e85d3ad1852
Get test_openAuth_can_refuse_None_uri to cleanup after itself

test_openAuth_can_refuse_None_uri sets the global
libvirt.allow_default_uri_connection to False but it leaves
it in this state which could cause test_tpool_execute_calls_libvirt
to fail if it ran immediately afterwards. This patch adds a cleanup
so _reset is called at the end of the test and not just if
another test in the same class is run after it.

Change-Id: I9762fcb81b2318beeb056c67bd9172056e1449ab
Closes-Bug: 1258553
Remove unused variables in neutron api interface and neutron tests

My local pyfakes checker in my editor keeps pointing these out
each time I save these files so I'd like to stop the messages.

Change-Id: I45a24af11434914be684d0944b49f4f746d48de4
Merge "Remove unused variables in neutron api interface and neutron tests"
Merge "Add extra_resources field to compute_nodes table"
Merge "Allow configuring the wsgi pool size"
Merge "Get test_openAuth_can_refuse_None_uri to cleanup after itself"