Use POST in bulk-delete

The DELETE verb applies to a single resource, and doesn't define any
semantics for the body.

http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.7

The swift Bulk Delete command affects multiple resources specified in a
DELETE body.

http://docs.openstack.org/developer/swift/misc.html#module-swift.common.middleware.bulk

While Bulk Delete is a welcome operation, its usage of DELETE is
unusual: affecting multiple resources and relying on reading content.

More typically, such an operation employs POST (or PUT), which folks
including api-craft usually agree is the best "catch-all" verb for
behaviors such as those affecting multiple resources. That's the TL;DR;
of the thread below.

https://groups.google.com/forum/#!searchin/api-craft/Regarding$20Bulk$20actions/api-craft/wY-W1NdZDRs/7YDwMhCR608J

Note that this topic isn't nasal or abstract. The current behavior is
unsupported using the built-in java http client. Even if third-party
libraries can work around this behavior, it is probably best to not be a
snowflake wrt http verb semantics where possible!

http://stackoverflow.com/questions/9100776/http-delete-with-request-body-issues

DocImpact

Closes-Bug: #1232787
Change-Id: I0fc74c85618fe4dd7ff5e7f9756c7f6f67aa0465
Merge "Use POST in bulk-delete"