Keystone; Automatic deletion of containers.
Keystone-client package optional.
Log error if keystone authentication requested but module not found
Fix flake8 warnings, add tox.ini
Check target container ACL

Some middlewares are not checking ACLs, for example formpost.

This patch compares the ACL of the target container and denies access if the
requesting user is not allowed to access the target container.
Add support for tempurl & formpost

The user is unknown if a request is authenticated using tempurl or formpost. In
this case we know that the request is authenticated for the original account,
thus we can check if an ACL for that account matches and grant access in this
case.
Strip reseller_prefix from account name when verifying tempurl ACL
Fix formpost support
Merge branch 'check-acl' of https://github.com/cschwede/swift-containeralias