ipvs.py: Add transport specifier to cluster name.

In some cases, for instance when loadbalancing DNS, it may make sense to
have both a UDP and a TCP cluster definitions servicing the same IP and
port on both transport protocols. This was poorly supported before, as
these two clusters' values would be published to the same metric.

This patch prepends all cluster names with their transport protocol and
an underscore, to allow this distinction.
ipvs.py: Also collect current connection counts.

This patch adds collection of the current counts of active and inactive
connections, both per backend and the total counts for the virtual
instance. This depends on an additional run of ipvsadm, as this info
cannot be obtained simultaneously with the --stats argument.

Please note that for setups using Direct Server Return, the active
connection counts will tend to be zero.
Merge pull request #469 from nyerup/master

IPVS collector: Add transport specifier to cluster name, also collect current connection counts.