Allow user to pass "headers" argument to the upload_* methods in the storage
API.

This way user can specify CORS headers with the providers which supported that.

Closes #404

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
AWS: Fixes the c3.X instances to have the proper disk size

Signed-off-by: Sebastien Goasguen <runseb@gmail.com>

This closes #405