Improve support for multiple remote addresses

Summary:
Currently, if a proxy declares more than one remote address,
the separator needed to be a comma.

But Squid documentation provides a syntax with spaces.

To provide a better support, this change explodes the IP address
with several delimiters, comma and whitespaces (\r \n \t \f and space).

Test Plan: New tests provided

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1638