AuthN support for Quantum

Adds authentication support for Quantum.  Generates a context object
and stuffs it into the 'quantum.context' variable in the WSGI environment.
This will be used in conjunction with authZ, later.

Partially implements blueprint authorization-support-for-quantum.

Change-Id: I8af171c2f11a08db5ee41e609d60ad203548650d
Add API v2 support

* Implements BP v2-api-melange-integration
* Adds v2 Plugin specification
* Refactors SQLAlchemy usage for multiple BASE's

Change-Id: I45f008f181c18269afdfe4a9b589a7c5ae56d225
Security group and policy identifiers added upto cassandra
policy_entry_list managed by user-agent updated as singleMetaValue to cassandra
n/w, sg, pol, pe_list all added in sequence per v2 api upto cassandra
new url scheme (vn in extensions; refactor ifmap interface; use lxml for parsing data read from ifmap server
works with api server; authentication works with keystone
checkpoint upto nova boot to work
merge to latest in openstack-quantum
net-create+list subnet-create+list works with api-server
plugin ini file creation
handle zero ref + skeleton for cfg parse
checkpoint implementing ports_list
quantum working with nova + vnc
correct filter handling in listing networks; catch NoIdError on name to id query
Updated IFMap schema related quantum changes
some more fixes after schema renaming. with this vm launched again successfully
Derive plugin from db_base_plugin_v2.QuantumDbPluginV2; refactor to provide all fields of a resource as expected by quantum-api
allocate id for subnet (locally stored for now); subnet read/delete working
add ipam extension skeleton. extend networks to have instance + references attribute. other refactoring for uniformity