ganglia: export $cname when ganglia_new is used

Currently, this happens:
- esams (& codfw)  hosts include ganglia, but this actually includes
  ganglia_new being used and $::ganglia::cname is never exposed.
- monitoring::ganglia uses $::ganglia::cname for passing $ARG7, which in
  turn passes the -C argument to check_ganglia. This is empty for esams
  hosts.
- check_ganglia uses -C (and -H, because of -q) as an argument to pass
  to gmetad's query interface (/cluster/hostname).
- For esams hosts, gmetad gets passed "//hostname" and instead of
  returning nothing, returns the full XML dump of every host instead
  (currently weighting 34MB).

=> icinga queries esams text caches by fetching 34MB 52 times every 5
minutes. Ugh.

Hack this around by re-exporting ganglia_new's $cname to
$::ganglia::cname. This is ugly, but a quick hack to fix a much bigger
problem.

Change-Id: I37d8ea79498bac46db983f2ea532c86034bc1e6e