Add exported flag to exposed test runtime receivers

Android T allows apps to declare a runtime receiver as not exported
by invoking registerReceiver with a new RECEIVER_NOT_EXPORTED flag;
receivers registered with this flag will only receive broadcasts from
the platform and the app itself. However to ensure developers can
properly protect their receivers, all apps targeting U
and registering a receiver for non-system broadcasts must
specify either the exported or not exported flag when invoking
registerReceiver; if one of these flags is not provided, the
platform will throw a SecurityException. This commit updates
the receivers in MainInteractionSession with the RECEIVER_EXPORTED
flag to maintain the current behavior of the test.

Bug: 268178696
Test: install and launch the apk in device with Android U.
Change-Id: I280e47f2a3557a8a8eb304bf45db75766170468a