The 'policies' parameter for the os-server-groups API is an array
for legacy reasons, but the schema validation allows only a single
item and it's from the enumerated list, and exactly one must be
specified when creating a server group.
This patch cleans up the policies parameter description to avoid
confusion over the number of items that can be specified or their
form, and it also provides a description of each available policy.
Since the jsonschema for policies is a bit confusing too, this
patch adds a comment in the schema code to avoid future confusion
over how the validation works.
Change-Id: I3ab2880ed6e8bb2cdf476c197719b83d768d44d0
Closes-Bug: #1652943
0a3f5dca2c