XenAPI: Fix new useage of trueorfalse

* Ensure that Xen setup scripts will continue to function when unset
  variables are used in stackrc
* Ensure that the generic functions are sourced in all places that xenrc
  (which sources stackrc) is sourced.

Change-Id: I54eba20733c2e149621b74a1387f0bef14fca12e
Embrane Plugin Support

Implements blueprint embrane-plugin-support

This commit implements Embrane's Neutron plugin installation support
in Devstack.
This is an extension of the openvswitch installation module, which is
used by the main plugin, and enables configuration by localrc

Change-Id: Ia4824f8d2300bcdce170d226145bbce6088f1557
s3_token has been moved to keystoneclient.

Change-Id: I6ffe756d517d11f323bd0c5d3b877d9a9f739a3b
read_password needs to store in .localrc.auto if local.conf is used.

when running stack.sh with no passwords in local.conf
read_password() creates localrc and local.conf is ignored

Change-Id: I25ad07569d2b42b190449591d5a01ade8022392c
Merge "Embrane Plugin Support"
Merge "s3_token has been moved to keystoneclient."
Merge "read_password needs to store in .localrc.auto if local.conf is used."
Merge "XenAPI: Fix new useage of trueorfalse"
Merge branch 'master' of https://github.com/openstack-dev/devstack