Clear binder identity when checking shell proxy permissions

We have an API to perform privileged ops only the shell can
do from a test. These were not wroking for instant tests as
we have rules based on calling UID whether an instant app,
in this case the caller, can see other apps, in this case the
shell.

bug:123086496

Test: cts-tradefed run cts-dev --enable-parameterized-modules --module-parameter instant_app -m CtsAppOpsTestCases

Change-Id: Ia3f9e8d9fe9c5e0dfad413222fd006c365778c5a