(PUP-2700) Fix double uri escape

The resolution of PUP-1892 caused percent encoding of file_content requests to
be doubled. This created a regression where Puppet file servers would respond
with a 404 not found status unless multiple decode operations were applied.

This patch fixes the issue by building the file_content indirector request
directly from the file source parameter instead of casting it to an escaped
URI. The `Indirector::Request` class handles the necessary URI escaping during
initialization.

Also, the test cases for fetching file content from a remote source have been fixed up and de-duplicated.
I like reducing these contents by several orders of magnitude. For consistency, perhaps change the one at line 335 as well? That way, future readers of this file don't ask "well, why is *this* one 10000 when the others are 10?"