Add "%I" (instance name) to application log formats

Summary:
Ref T12611. Currently, the HTTP/SSH logs don't have an option to include the instance name.

Add such an option.

Leave it out of the default logs because most installs don't use this.

Test Plan: See next changes.

Reviewers: chad, amckinley

Reviewed By: chad

Maniphest Tasks: T12611

Differential Revision: https://secure.phabricator.com/D17776