R1:458a28eed3a0

Truncate `logSource` in Harbormaster to the database column limit

Summary: This can be a command, which might be arbitrarily long, but the column is VARCHAR(255).

Test Plan: `grep`

Reviewers: dctrwatson, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D8446