Add API to check for emulated external storage

When the storage is emulated, we don't want to install ASEC containers
to it. This adds the API to check when the external storage is emulated
and uses it to check whether or not to install packages to the external
storage in an ASEC container.

Bug: 3024387
Change-Id: Ia0318aca9e4938a4897deaada5603a4c7c1d0f48
diff --git a/libs/storage/IMountService.cpp b/libs/storage/IMountService.cpp
index 3ad9319..17a961b 100644
--- a/libs/storage/IMountService.cpp
+++ b/libs/storage/IMountService.cpp
@@ -47,6 +47,7 @@
     TRANSACTION_unmountObb,
     TRANSACTION_isObbMounted,
     TRANSACTION_getMountedObbPath,
+    TRANSACTION_isExternalStorageEmulated,
 };
 
 class BpMountService: public BpInterface<IMountService>