Pass a list of metric readers (#1124)

Fixes #1123

Author: ocelotl

instrumentation/opentelemetry-instrumentation-system-metrics/src/opentelemetry/instrumentation/system_metrics/__init__.py

@@ -49,7 +49,7 @@
 
     exporter = ConsoleMetricExporter()
 
-    set_meter_provider(MeterProvider(PeriodicExportingMetricReader(exporter)))
+    set_meter_provider(MeterProvider([PeriodicExportingMetricReader(exporter)]))
     SystemMetricsInstrumentor().instrument()
 
     # metrics are collected asynchronously