Description of Problem:
HA Cluster PMDA PM_TYPE_STRING metrics are unable to export their values through the pmproxy OpenMetrics API due to String type metrics being unsupported. 

The Pacemaker Location Constraint details are required to be able to pinpoint primary node. These location constraints need to be added as Labels in order to be exposed during export.

Version-Release number of selected component (if applicable):
pcp-5.2.5-3

How reproducible:
Always

Steps to Reproduce:
1.) Install pcp-pmda-hacluster
# yum  install -y pcp pcp-pmda-hacluster

2.) Start pmcd service, install PMDA and start pmproxy Service
# systemctl start pmcd
# ./usr/libexec/pcp/pmdas/hacluster/Install
# systemctl start pmproxy

3.) Check for location constraints data in pmproxy output
# curl http://localhost:44323/metrics?names=ha_cluster.pacemaker | grep location_constraints

Actual Results:
Output of "curl" is as follows:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 25835    0 25835    0     0  43714      0 --:--:-- --:--:-- --:--:-- 43714
...

Expected Results:
The output should provide the location constraint information for pacemaker

Additional info:
Plan on adding the required location constraints data as labels to a new metric which
will be of a supported OpenMetrics data type in pmproxy.