Check current user owns a frp credential

In Android U+ tablet device, Android introduces headless mode which
running on a main user instead of system user. Therefore, device throw
a security error in HSUM build now.

For now, we check whether current user owns a frp
credential instead. This way also works on non HSUM build.

Test: robo test + run FRP mode in Suw flow.
Fix: 262438904
Change-Id: Ie4c7c470b13b9de8d532e61e9984521cebe7adff