ganglia: fix some missing paths for labs

The ganglia-webfrontend Ubuntu package we provide no more ship the PHP
files. Instead one has to install the sources manually.

Doing so I noticed a few issues:
- conf.php is expected as conf_default.php, a symlink fix it
- we need a version.php file setting up some global
- a few directories under /var/lib/ganglia are missing and need to be
  writable by Apache

This patch at least bring something more or less working on
http://ganglia.wmflabs.org/ and has been applied manually already on
aggregator.eqiad.wmflabs.

Bug: 63362
Change-Id: I8e1df63c8e8d250f8b29a5390360f825d0838829
Merge "ganglia: fix some missing paths for labs" into production