Repurpose KeystoneWorkers add keystone::wsgi::apache::threads

Repurpose KeystoneWorkers add keystone::wsgi::apache::threads

Now that keystone is run with wsgi apache the KeystoneWorkers
param has no efffect [1]. This repurposes KeystoneWorkers to now
set wsgi::apache::workers and adds the
keystone::wsgi::apache::threads hardcoding to 1 (can overrride
via extraconfig data)

[1] https://github.com/openstack/puppet-keystone/blob/51c68fb127c28b9748b352871783c3ec6ef5c83b/manifests/init.pp#L396

Closes-Bug: 1598092
Change-Id: I503d1f0d3f4c56abfaf4609ea8290e78668013b6