Enable HTTP protocol for storage

[itamarst]

The HTTP protocol is designed to be used by default, with a config switch to disable it. For now, however, it's disabled by default, but at some point we'll want to flip the switch.

Places to update:

• The code that reads force_foolscap in node.py should default to it being False.
• force_foolscap config option should be documented.
• Default version for _create_node() in integration tests.
• ... search codebase for references to this ticket ...