(POOLER-170) Revise vmpooler usage stats

Break down the usage stats into smaller groups so as to manage the
number of stat lines collected for Prometheus.

This may need some further revision to filter out Litmus stats, or
otherwise collect litmus usage information.

spec/unit/promstats_spec.rb

@@ -142,22 +142,42 @@ describe 'prometheus' do
           po.get(labels: metric[:labels])
         }.by(1)
       end
-      it 'Increments usage.#{user}.#{poolname}' do
+      it 'Increments user.#{user}.#{poolname}' do
         user = 'myuser'
         poolname = 'test-pool'
-        expect { subject.increment("usage.#{user}.#{poolname}") }.to change {
-          metric, po = subject.get("usage.#{user}.#{poolname}")
+        expect { subject.increment("user.#{user}.#{poolname}") }.to change {
+          metric, po = subject.get("user.#{user}.#{poolname}")
           po.get(labels: metric[:labels])
         }.by(1)
       end
-      it 'Increments label :user' do
-        # subject.increment(:user, :instance, :value_stream, :branch, :project, :job_name, :component_to_test, :poolname) - showing labels here
-        pending 'increment only supports a string containing a dot separator'
-        expect { subject.increment(:user) }.to change {
-          metric, po = subject.get(:user)
+      it 'Increments label usage_jenkins_instance.#{jenkins_instance}.#{value_stream}.#{poolname}' do
+        jenkins_instance = 'jenkins_test_instance'
+        value_stream = 'notional_value'
+        poolname = 'test-pool'
+        expect { subject.increment("usage_jenkins_instance.#{jenkins_instance}.#{value_stream}.#{poolname}") }.to change {
+          metric, po = subject.get("usage_jenkins_instance.#{jenkins_instance}.#{value_stream}.#{poolname}")
           po.get(labels: metric[:labels])
         }.by(1)
       end
+      it 'Increments label usage_branch_project.#{branch}.#{project}.#{poolname}' do
+        branch = 'treetop'
+        project = 'test-project'
+        poolname = 'test-pool'
+        expect { subject.increment("usage_branch_project.#{branch}.#{project}.#{poolname}") }.to change {
+          metric, po = subject.get("usage_branch_project.#{branch}.#{project}.#{poolname}")
+          po.get(labels: metric[:labels])
+        }.by(1)
+      end
+      it 'Increments label usage_job_component.#{job_name}.#{component_to_test}.#{poolname}' do
+        job_name = 'a-job'
+        component_to_test = 'component-name'
+        poolname = 'test-pool'
+        expect { subject.increment("usage_job_component.#{job_name}.#{component_to_test}.#{poolname}") }.to change {
+          metric, po = subject.get("usage_job_component.#{job_name}.#{component_to_test}.#{poolname}")
+          po.get(labels: metric[:labels])
+        }.by(1)
+      end
+
       it 'Increments connect.open' do
         expect { subject.increment('connect.open') }.to change {
           metric, po = subject.get('connect.open')