blog: bump max backend connections to 256

maxconnections 100 is too low, considering Apache can handle much more
than that. Raise it to 256.

Additionally, the Varnish config reload was failing because of
referencing an undeclared ACL, ssl_proxies. Fix that in the main Varnish
config by removing an if block and defining the ACL, even if it's empty.

Change-Id: I42f3f2bc6eb6b3e4ab66875072a170752b6280e8