Switches to the existing guest instead of failing.

Fixes the issue when any subsequent switches to non-ephemeral guests
fail repeatedly.

Change-Id: I0b82f52fa431440fce29cf7e52c92da9e25cfcb7
Fixes: 116141567
Test: atest CarUserManagerHelperTest
(cherry picked from commit 821061ca5e434ac2b6c0a5168e066b7348860aeb)
2 files changed