findmissing: Use UNION to query multiple fixes tables

Use sql UNION statement to query multiple fixes tables instead of
querying each table and combining the results.

BUG=None
TEST=Run "findmissing status sha sha ..."

Change-Id: I5e1693d9df8b8728f42cdfe61d412db0ab1a7540
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2318408
Tested-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Curtis Malainey <cujomalainey@chromium.org>
Commit-Queue: Guenter Roeck <groeck@chromium.org>
2 files changed