Revert "app: Use a ThreadPool to fetch metrics."

Using multiprocessing is at least causing mod_wsgi to throw a hissy fit.
A few other WSGI servers seem to be able to deal with this correctly but
for now, back to serial requests.

puppetboard/app.py

@@ -9,7 +9,6 @@ try:
 except ImportError:
     from urllib.parse import unquote
 from datetime import datetime, timedelta
-from multiprocessing.dummy import Pool as ThreadPool 
 
 from flask import (
     Flask, render_template, abort, url_for,
@@ -92,17 +91,19 @@ def index():
     # TODO: Would be great if we could parallelize this somehow, doing these
     # requests in sequence is rather pointless.
     prefix = 'com.puppetlabs.puppetdb.query.population'
-    pool = ThreadPool()
-    endpoints = [
-                "{0}{1}".format(prefix, ':type=default,name=num-nodes'),
-                "{0}{1}".format(prefix, ':type=default,name=num-resources'),
-                "{0}{1}".format(prefix, ':type=default,name=avg-resources-per-node'),
-                ]
-    fetched_metrics = pool.map(puppetdb.metric, endpoints)
+    num_nodes = get_or_abort(
+        puppetdb.metric,
+        "{0}{1}".format(prefix, ':type=default,name=num-nodes'))
+    num_resources = get_or_abort(
+        puppetdb.metric,
+        "{0}{1}".format(prefix, ':type=default,name=num-resources'))
+    avg_resources_node = get_or_abort(
+        puppetdb.metric,
+        "{0}{1}".format(prefix, ':type=default,name=avg-resources-per-node'))
     metrics = {
-        'num_nodes': fetched_metrics[0]['Value'],
-        'num_resources': fetched_metrics[1]['Value'],
-        'avg_resources_node': "{0:10.0f}".format(fetched_metrics[2]['Value']),
+        'num_nodes': num_nodes['Value'],
+        'num_resources': num_resources['Value'],
+        'avg_resources_node': "{0:10.0f}".format(avg_resources_node['Value']),
         }
 
     nodes = puppetdb.nodes(