Do not clear a shared user's permissions on an app install.

When regranting permissions for an app during an install if
that app is in a shared user we should not clear the permissions
as the permissions for the shared user are additive and go away
when apps requesting them are uninstalled.

bug:20050689

Change-Id: I82aa70669fc25a45e7020a1545b093db5525f5cf
diff --git a/services/core/java/com/android/server/pm/PackageSetting.java b/services/core/java/com/android/server/pm/PackageSetting.java
index a3f4c0b..e7c0ef7 100644
--- a/services/core/java/com/android/server/pm/PackageSetting.java
+++ b/services/core/java/com/android/server/pm/PackageSetting.java
@@ -74,4 +74,8 @@
     public boolean isSystem() {
         return (pkgFlags & ApplicationInfo.FLAG_SYSTEM) != 0;
     }
+
+    public boolean isSharedUser() {
+        return sharedUser != null;
+    }
 }