Don't create cache when doing Apex PreRebootVerification

When StagingManager uses PackageParser2 to parse the APEX files during
pre-reboot verification with the parse flag PackageManager.GET_META_DATA,
it creates the caches of them. But, the caches are not used. Pass the
"null" instead of mCacheDir to avoid creating the caches.

Test: manual
Fix: 153618582
Change-Id: I40676082fc98d87ad2ad9fc94d02903afe0243d4

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

@@ -3576,7 +3576,8 @@ public class PackageManagerService extends IPackageManager.Stub
             // Prepare a supplier of package parser for the staging manager to parse apex file
             // during the staging installation.
             final Supplier<PackageParser2> apexParserSupplier = () -> new PackageParser2(
-                    mSeparateProcesses, mOnlyCore, mMetrics, mCacheDir, mPackageParserCallback);
+                    mSeparateProcesses, mOnlyCore, mMetrics, null /* cacheDir */,
+                    mPackageParserCallback);
             mInstallerService = new PackageInstallerService(mContext, this, apexParserSupplier);
             final Pair<ComponentName, String> instantAppResolverComponent =
                     getInstantAppResolverLPr();