Fix pool statistics for LBaaS Haproxy driver

Total connections was mapped to none of the counters
of haproxy. Active connections was mapped to active request
counter(qcur)) of haproxy which in low load situations
always remains zero.

Patch maps connections API counters to haproxy session counters
and fixes unit test accordingly.

Change-Id: I0ef4f76a75340232eb11a9b95453769ecd89d13a
Closes-Bug: #1319361
Merge "Fix pool statistics for LBaaS Haproxy driver"