Delete the install-server::caching-proxy class

No reason for a class that only includes another class, move that squid3
class definition in the role and the configuration file alongside it.
Update RSpec, tests and while at it fix an omission in RSpec

Change-Id: I3cca79d0db40eb10c5ce17c8d29a350a84d89643
Merge "Delete the install-server::caching-proxy class" into production