Add missing requirements
Add missing requirements

WebOb is needed in our code[1].

[1]https://github.com/openstack/watcher/blob/master/watcher/api/
middleware/parsable_error.py#L70

Change-Id: I6dd3940057368ff70656dd40c75ec59284f378bf

stackforge/watcher,stackforge/watcher,openstack/watcher,openstack/watcher