MINOR: http-ana: Add option to keep query-string on a localtion-based redirect

MINOR: http-ana: Add option to keep query-string on a localtion-based redirect

On prefix-based redirect, there is an option to drop the query-string of the
location. Here it is the opposite. an option is added to preserve the
query-string of the original URI for a localtion-based redirect.

By setting "keep-query" option, for a location-based redirect only, the
query-string of the original URI is appended to the location. If there is no
query-string, nothing is added (no empty '?'). If there is already a
non-empty query-string on the localtion, the original one is appended with
'&' separator.

This patch should fix issue #2728.