If the user specifies --web-server-user on the `rb-site install`

CLI or a distribution packager has set a default web server user

in rb_platform.py, `rb-site install` will attempt to chown the

necessary web-facing directories and their contents to that user.
If it succeeds in chowning all such directories, `rb-site install`

will now suppress the summary lines telling the user what

directories need to be manually owned.
If it fails on one or more ownership changes (or if no ownership

change is attempted due to a lack of a user or running on Windows),

then the original notice of directories to update is displayed at

the end of installation.

I deployed several Review Board sites as root against a PostgreSQL database:

DEFAULT_WEB_SERVER_USER="" in rb_platform.py, --web-server-user=apache on the CLI

  *- All appropriate directories were owned by apache:apache at the end of deployment. All other directories were owned by root.
DEFAULT_WEB_SERVER_USER="" in rb_platform.py, --web-server-user not on the CLI

  *- All directories were owned by root at the end of deployment
DEFAULT_WEB_SERVER_USER="apache" in rb_platform.py, --web-server-user not on the CLI

  *- All appropriate directories were owned by apache:apache at the end of deployment. All other directories were owned by root.