Override iisnode log settings from the portal when hosted in a Windows Azure Web site

[glennblock]

1. If logging is enabled in the portal, but disabled in iisnode.yml / web.config then the portal should win.
2. If logging is disabled in the portal (default), but enabled in iisnode.yml / web.config then logging should be enabled.

[tjanczuk]

That modality is somehow confusing. How about:

1. If logging is explicitly configured in iisnode.yml, it always wins, regarding of whether enabled or disabled.
2. Otherwise (i.e. if the dev did not say anything about logging in iisnode.yml), portal setting is effective.

[glennblock]

The only concern I had there is we explicitly disable it today in the iisnode.yml that we generate using our cli.

[tjanczuk]

This is a dupe of #220