Use curl to download package from github.

Github recently removed some sslv3 ciphers - wget seems to only
enable a subset of the ciphers available so fails now, but curl
continues to succeed.
Also tune squid cache settings to ignore certain file extentions
and cache only rpm and debian packages

Change-Id: Id46df19ee51e9a771dbd47bd5643af9007669385
Closes-bug: #1342995