Regress a few changes from this branch until unix socket support is fully embraced —
* Maintain current keosd *-server-address config names
* Have keosd start HTTP server by default still (though this time on 8900)
* Change cleos default URL back to http://127.0.0.1:8900

Also add customization method for defaults based on nodeos vs keosd

Self-register wallet_plugin.
Fix tests by adding config-dir argument to walletd launch options.