OVH's Swift applies a rate limit on the authentication.
attachment_swift authenticates again each time it has to read/write an
attachment. When running upgrades on upgrades of files or installing a
new DB, at some point, we get rejected with HTTP 429.
This commit introduces a shared storage for Swift Session. All
connections will reuses the same authentication token created the first
time a connection needs a Session.
Note: needs python-swiftclient>=3.7.0 to have
https://github.com/openstack/python-swiftclient/commit/1971ef880ff225379d4a91f00f89f323a1605eeb
Guewen Baconnier
jcoux