Fallback should be evaluated for each preference

1) alowFallback flag was incorrectly not reset while setting profile
   preference. Corrected it.

2) Threw exception if default preference and enterprise preference are
set together

3) renamed clearUser to withoutUser

Bug: 231670730
Test: ConnectivityServiceTest

Change-Id: If92ebe0cc23f18c8808893926d5e1d12ff2e3650
Merged-In: Iaf49237bdc791c7e1dd884d069eff64e74757477
3 files changed