Clear calling identity when accessing isProfileOwner and listAllOwners

Last year we added a security fix ag/12968597 to address
b/153995973. Now, some DPM methods require the interact
across users permission, unlike in R. This CL aims to
prevent potential security exceptions in these methods
by clearing their calling identity.

Bug: 182279073
Test: atest DevicePolicyManagerTest
Change-Id: Ie861a7880160563f9613db72e3283edac294a7a1