Fix a deadlock in AccountManagerService cause by different

paths of code getting the mCacheLock and DB locks in different
orders.

The philosophy I followed for this was to ensure that the
DatabaseHelper is only ever accessed from within a
synchronized(mCacheLock) block. I also renamed a bunch of
methods to make it easier to know if a given method should
be called from within this synchronized block.

Bug: 3404506
Change-Id: Ia48f95e77b77647d0717f70f1d8364da3719cc13