Provide a "-f" flag to scripts/sql/upgrade_schema.php

Summary: Normally this gives you a prompt about taking down services, provide a noninteractive mode for scripting the upgrade process.

Also drop a generally bad/confusing/irrelevant piece of advice from the documentation and replace it with information about -f.

Test Plan: Ran with and without -f. Ran with -h.

Reviewers: moskov, tuomaspelkonen, jungejason, aran

CC:

Differential Revision: 387