Allow setting gmcast.peer_timeout value

In some resource constrained environments particularly during deploy
time percona-cluster nodes can experience time outs during inter-node
communication.

This changes makes the gmcast.peer_timeout configurable based on the
galara cluster documentation:
http://galeracluster.com/documentation-webpages/galeraparameters.html

Warning: Changing this value from the default may have unintended
consequences. This should only be used when constraint's call for it.

Closes-Bug: #1742683
Change-Id: If93d6ba9d0e99b6af59358a7f3ea40e3aa2a6dbc

hooks/percona_hooks.py

@@ -108,6 +108,7 @@ from percona_utils import (
     LeaderNoBootstrapUUIDError,
     update_root_password,
     cluster_wait,
+    get_wsrep_provider_options,
 )
 
 from charmhelpers.core.unitdata import kv
@@ -197,11 +198,14 @@ def render_config(clustered=False, hosts=None):
         # See lp 1380747 for more info. This is intended as a stop gap until
         # percona package is fixed to support ipv6.
         context['bind_address'] = '::'
-        context['wsrep_provider_options'] = 'gmcast.listen_addr=tcp://:::4567;'
         context['ipv6'] = True
     else:
         context['ipv6'] = False
 
+    wsrep_provider_options = get_wsrep_provider_options()
+    if wsrep_provider_options:
+        context['wsrep_provider_options'] = wsrep_provider_options
+
     context.update(PerconaClusterHelper().parse_config())
     render(os.path.basename(config_file),
            config_file, context, perms=0o444)