Let haproxy_defaults be overridable
Let haproxy_defaults be overridable

Add the haproxy_defaults_override parameter so the defaults_options
in haproxy are overridable. Tested by adding the following yaml to
the deployment:
parameter_defaults:
  ExtraConfig:
    tripleo::haproxy::haproxy_defaults_override:
      retries: 7

Observed that haproxy.conf contained the following (retries defaults
to 3):
defaults
  retries  7

Change-Id: I52b8f528e334e4d243ac7f506b9f293dab9f478d
Closes-Bug: #1732176

openstack/puppet-tripleo,openstack/puppet-tripleo,openstack/puppet-tripleo