scanner: allow microsoft appcenter, except appcenter-push

This sdk is open source. It was added because appcenter has a dependency
to play-services. It's possible though to build an app using appcenter
that doesn't pull in play services, so we can't blanket ban the sdk.

The appcenter-push modules has obvious refenrences to firebase, so it's
safe to error on that.

Ref: https://phabricator.wikimedia.org/T254980

fdroidserver/scanner.py

@@ -86,7 +86,7 @@ def scan_source(build_dir, build=metadata.Build()):
             r'''["']com.facebook.android['":]''',
             r'cloudrail',
             r'com.tencent.bugly',
-            r'com.microsoft.appcenter',
+            r'appcenter-push',
         ]
     }