Add API ref for FlavorDisabled extension

Added a new section, which should be accessible via
http://api.openstack.org/api-ref-compute.html#os-flv-disabled
(after change merged)
which shows the sample responses in this directory:
api-ref/src/wadls/compute-api/src/api_samples/OS-FLV-DISABLED

More about the 'disabled' filed in 'flavor'
http://openstack.markmail.org/thread/zi7bkeqlnjbtkz5t

Patch2:
added missing file os-flv-disabled.wadl

Patch3:
Using sentence-style caps for titles

Use <literal></literal> tag to surround OS-FLV-DISABLED:disabled

Change tenant_id to be of type "xsd:string" from the name space
xmlns:xsd="http://docs.rackspacecloud.com/xsd/v1.0"

Change-Id: Ida174590303b46fe7c8b2ca4ce26a1632daf2762
backport: havana
Closes-Bug: #1089019