SubscriptionController: load all subs before setting defaults

Switch the whole class to use the new inserted SIM logic added in
change id Iab1225c83b508e055d8a8de55c1e21e2aa153ca5. The previous patch
fixed scenarios going from two sims to one, but going from one to two
(or switching between two sims) is still not working right as the
addSubInfoRecord() still used getActiveSubInfoCountMax() to determine
the number of SIMS.

 - Update getActiveSubInfoCountMax() to return the correct number of SIMs.

 - Furthermore, we need to _only_ update our subscription defaults if we
   are sure we are not in the middle of an update.

 - Let the subscription controller set defaults for 1 SIM device after
   we're done loading

Change-Id: I28eefaff61ae7c75732641465ca59eb67cf3e198
Ticket: CYNGNOS-2185, CYNGNOS-2570