Allow HEAD for POST tempurls

HEAD requests are already allowed for GET and PUT tempurls; this
commit adds that for POST tempurls. Since POST replaces all the
object's metadata, it's quite useful to be able to HEAD the object in
order to fetch the old metadata and do a client-side merge of the new
metadata (like with normal, token-authenticated POST requests).

Change-Id: I603c7822cd27f0e304fd27024f83f95114eb0aef
Make swift-form-signature testable

Moved the body of bin/swift-form-signature into
swift/cli/form_signature.py, like was done with swift-ring-builder and
others. Added a couple basic tests; there's not 100% coverage, but
it's better than the 0% coverage we had before.

It's almost a straight forklift, but I changed exit() calls to return
statements.

Change-Id: Ie2f702c070da24d9cdface83b9e838e9e2965085
Merge "Allow HEAD for POST tempurls"
Bail out a little faster when object write affinity is off

This function was calling a couple functions prior to checking for
early bailout; if it did bail out, the results of those function calls
were unused. Bail out earlier to avoid wasted work.

Change-Id: Ia023549a45355b44ebfb41212565c42f993415a9
Update the swift documentation theme

Currently the theme used by the swift developer docs are out of
date, it should be using oslosphinx, to provide a similar look
and feel between all openstack related projects.

Change-Id: Id7c226cdc13c6c4f3b5082b1ef4dfe09966b21ec
Merge "Bail out a little faster when object write affinity is off"
Make swift-form-signature output a sample form

swift-form-signature would give you the required expiration-time and
HMAC signature, but it wouldn't help you actually construct the HTML
form. To do that, you had to go look at the formpost middleware's doc
string and make up a form yourself.

For convenience, this commit makes swift-form-signature output a
sample form with the computed values filled in already; the user only
needs to fill in the Swift cluster's hostname.

Change-Id: I70d70a648b78b382dbfbe8ff918e6158a7f6a0ab
Merge "Update the swift documentation theme"
Merge "Make swift-form-signature testable"
Merge "Make swift-form-signature output a sample form"