init: wait_for_prop shouldn't run in a subcontext

wait_for_prop sets a flag that prevents the action queue from
continuing while otherwise allowing init's main loop to continue
executing.  This cannot be done from a subcontext, so it's moved to
normal init.

All property functions need work in any case, particularly once
property_service is moved out of init.

Bug: 62875318
Test: boot sailfish and see that the previous failure related to this
      is fixed

Change-Id: Ib9e0d0bdbd0ff22ab0e5c3fe6db620700af266c6