(PUP-2631) Elide long URIs for 404 message

When the agent encounters a 404 response from the master and it has been told
to fail on 404, it previously output the entire path plus query string that
it requested. However, the most common case where this occurs is when
requesting a catalog, which can have a very long query string if the request
was done with a GET. This does not always occur because even longer query
strings will result in the agent using a POST instead of a GET, which causes
the long query string output problem to go away.

In order to fix this the query string is now elided to 100 characters
(97 characters of the original text plus 3 periods).  In order to still be
able to debug any problems that might result from the query, however, the
query string is *not* elided if the log level is `debug`.