Don't allow shell to spoof initiating package name.

This preserves the ability to override the installer package name
(installer of record). But it prevents overriding the initiating
package name (real installing package) which should always be null for
an adb installed package.

Bug: 160224791
Test: manual
Test: atest PackageManagerTests PackageVerifierTest
Change-Id: I586b524d11dab075034ca05a87fac819cb99b61b

services/core/java/com/android/server/pm/PackageInstallerService.java

@@ -522,7 +522,9 @@ public class PackageInstallerService extends IPackageInstaller.Stub implements
 
         if ((callingUid == Process.SHELL_UID) || (callingUid == Process.ROOT_UID)) {
             params.installFlags |= PackageManager.INSTALL_FROM_ADB;
-
+            // adb installs can override the installingPackageName, but not the
+            // initiatingPackageName
+            installerPackageName = null;
         } else {
             if (callingUid != Process.SYSTEM_UID) {
                 // The supplied installerPackageName must always belong to the calling app.