(sensu#638) Enable multiple Sensu Enterprise Dashboard API endpoints

Without this patch it is not possible to manage multiple
sensu::enterprise::dashboard::api resources in the same datacenter
because the resources conflict over the namevar.  This patchset
addresses the problem by changing the namevar to the `host` and
establishing the `datacenter` attribute.

An example of how to exercise this behavior is located in
tests/sensu-enterprise-dashboard-multi-api.pp

resolves sensu#638
closes sensu#651
closes sensu#584

tests/sensu-enterprise-dashboard-multi-api.pp

@@ -0,0 +1,40 @@
+##
+# This class exercises the Dashboard API behavior in
+# https://github.com/sensu/sensu-puppet/issues/638
+# https://github.com/sensu/sensu-puppet/pull/651
+#
+# Usage:
+# Bring up the sensu-server Vagrant vm.
+# After provisioning completes, run:
+# puppet apply -v /vagrant/tests/sensu-dashboard-api.pp
+node 'sensu-server' {
+  # This configuration is expected to produce /etc/sensu/dashboard.json with the values of:
+  # name: example-dc
+  # host: sensu.example.com
+
+  if ! ($facts['se_user'] or $facts['se_pass']) {
+    fail 'Provide Sensu Enterprise Credentials using FACTER_SE_USER and FACTER_SE_PASS environment variables.'
+  }
+
+  # Avoid /etc/sensu/dashboard.d/.keep from install of
+  # sensu-enterprise-dashboard-1:2.8.1-1.x86_64 conflicts with file from
+  # package uchiwa-1:0.25.2-1.x86_64
+  package { 'uchiwa':
+    ensure => absent,
+    before => Class['sensu'],
+  }
+
+  class { '::sensu':
+    enterprise_dashboard => true,
+    enterprise_user      => $facts['se_user'],
+    enterprise_pass      => $facts['se_pass'],
+  }
+
+  sensu::enterprise::dashboard::api { 'sensu.example.com':
+    datacenter => 'example-dc',
+  }
+
+  sensu::enterprise::dashboard::api { 'sensu.example.org':
+    datacenter => 'example-dc',
+  }
+}