Extend tests utility belt

It's be nice to have some standard test wrapper with 'retry until' or 'pass if any of N' functionality to deal with things like:

```
Compact after lowering attachment size limit couchdb_attachments_tests:544: should_compact_after_lowering_attachment_size_limit...*failed*

in function couchdb_attachments_tests:wait_compaction/3 (test/couchdb_attachments_tests.erl, line 586)
in call from couchdb_attachments_tests:compact_db/1 (test/couchdb_attachments_tests.erl, line 573)
in call from couchdb_attachments_tests:'-should_compact_after_lowering_attachment_size_limit/1-fun-1-'/1 (test/couchdb_attachments_tests.erl, line 550)

**error:{assertion_failed,[{module,couchdb_attachments_tests}, {line,573},
{reason,"Timeout waiting for database database compaction"}]}
output:<<"">>
```

Start with test/couchdb_attachments_tests.erl, especially wait_compaction/3 and compact_db/1 in the failing example. Review the existing test helpers before deciding where reusable retry and “pass if any of N” behavior belongs. Done means the requested wrappers exist and address the intermittent compaction-test pattern.

Written by the indexing model from the issue text.