Code review comment for lp:~pieq/checkbox/fix-1585556-sanitizing-comments

I used the regex provided by Sylvain instead of the original one. This one includes all the escape characters that `CONTROL_CODE_RE_STR` was taking care of, so we just need one regex to rule them all.

This time, the whole sequence is escaped, not only the first part.

I also added a unit test that is used in DiskJobResultTests and MemoryJobResultTests.