Refine error behavior of `bin/search index`
Summary: Fixes T5991. If //all requested documents// failed to index, consider this a catastrophic failure and exit with an error code.
Test Plan:
- Ran `bin/search index --type TASK`, observed successful exit despite a small number of un-indexable documents.
- Ran `bin/search index PHID-TASK-xxx` for an invalid task, observed exception on exit after complete failure.
- Ran normal indexing through daemons.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T5991
Differential Revision: https://secure.phabricator.com/D14174