Add swift_store_ssl_compression param

Add a new glance-api.conf parameter 'swift_store_ssl_compression',
which allows disabling SSL layer compression for https swift requests.

This can increase performance when transferring compressed images (eg
qcow2) to/from swift.

Addresses bug 1190666.

DocImpact.

Change-Id: Ic26dba9dce5ea7e5c09fdd531746b93cec54fc5c
Merge "Add swift_store_ssl_compression param"