Allow setting default phone account handle per user

The problem we cannot have every users has their own user handle is becoz
we did not store user handle.
Store default phone account handle with user handle, so that every user
can has it owns default phone account handle.

Bug: 25941865

Change-Id: Iad8a920e9ceeb9caa8a7d8bc6a1d2f2dfc8dcd58