adapt squid redirector for the beta context

The squid C redirector uses /etc/squid/redirector.conf which is used to
rewrite some URL for the Mobile infrastructure. The regex needs to be
adapted for the beta cluster which uses 'beta.wmflabs.org.' as a domain
name whereas production is under 'org'.

This patch convert redirector.conf to an erb template
The $squid_redirector_tld parameter contains the domain name common to
all projects. It is escaped in the Regex just like we did in the varnish
configuration for bits.

Change-Id: Ia33e379817fd75676fd61d780a83d38963328e38
Merge "adapt squid redirector for the beta context" into production