In the "List allocation candidates" API,
the 'traits' parameter is missing.
So add it and update examples.
Change-Id: I4a307759f9e8fa80d003d92142f8e99b2c09c9fe
Partial-Bug: #1778670
JSON body examples of Placement API reference
are in the same directroy where *.inc files exist.
This patch moves JSON body examples to an isolated directory
in order to make it easier to maintain the API reference.
Change-Id: I8fd587100d22bd10dd4b2b2f1b25c5ecc7fc8537