1. The libxmlsec1-dev package is missing from the script (but exists on the Wiki page), which causes installation fails.
2. G++ 4.8 is required to build v8 engine which is required by nodejs used by edx-insights. But the offical Ubuntu 12.04 only provides gcc 4.6.3, so we should set ppa's tool chain and install gcc/g++ 4.8 before actual installation.

This is to deal with the issue pointed out in #2036