aws-sigv4: url encode the canonical path

aws-sigv4: url encode the canonical path

Refactors canon_query, so it could use the encoding part of the function
to use it in the path.

As the path doesn't encode '/', but encode '=', I had to add some
conditions to know If I was doing the query or path encoding.

Also, instead of adding a `bool in_path` variable, I use `bool
*found_equals` to know if the function was called for the query or path,
as found_equals is used only in query_encoding.

Test 472 verifies.

Reported-by: Alexander Shtuchkin
Fixes #13754
Closes #13814

Signed-off-by: Matthias Gatto <matthias.gatto@outscale.com>