bug 1512499 - handle psutil returning None for physical_cores. r=froydnj

psutil has a bug on arm systems where it will return None for physical_cores:
giampaolo/psutil#1359

This causes us to generate invalid telemetry data which raises an error. Fix
this by simply omitting the field in this case.

Differential Revision: https://phabricator.services.mozilla.com/D14969

UltraBlame original commit: be66f8877e465637de546fd3a94a55009e74f973

python/mozbuild/mozbuild/telemetry.py

@@ -177,7 +177,9 @@ def get_system_info():
         import psutil
 
         info['logical_cores'] = psutil.cpu_count()
-        info['physical_cores'] = psutil.cpu_count(logical=False)
+        physical_cores = psutil.cpu_count(logical=False)
+        if physical_cores is not None:
+            info['physical_cores'] = physical_cores