Fix race in dafault phone creation

ImsPhone might be created when we are starting monitoring IMS service.
When we are creating ImsPhone, we are opening IMS service.
When IMS service is being opened, it might request default phone (which
might not be ready yet).

Bug: 24130556
Change-Id: I7677b3131b15c78f6c6ac008f0cbb06b1a427b5d