stbt-batch.d/report.py: Allow Confluence-style links in Failure reason & Notes

Allow inserting links into "Failure reason" and "Notes" fields of a
test report in the following format:
    [<text>|<url>]
Example:
    [Issue 1|https://github.com/drothlis/stb-tester/issues/1]

These links are interpreted the follwing way:
- A test run's page contains clickable <text> that opens <url> in a
  new page.
- The table of test runs contains <text> in plain text format, as Failure
  reason and Notes are truncated to 30 characters. It would break the
  HTML page if they contained truncated `<a href="...` blocks.

Implementation issues:

`jinja2.Markup.escape` returns a `jinja2.Markup` object that
escapes the string at the end of the filter pipeline, after applying
the `linkify` filter, but we'd like to apply `escape` before `linkify`.
That's why the return value of `escape` is converted to string in
`Run.read`.

The funcion `testrun` needs the decorator `nose.tools.nottest`,
otherwise `nosetests` regards it as a test case as its name starts
with "test".