Fix cross-process race in initial files/cache dir creation

Apps that run components in separate processes, especially that
host providers in separate processes, can hit a race condition
where two processes simultaneously discover that the files/cache
dir must be created, then each calls mkdirs().  One of these will
fail not because the dir couldn't be created, but because it lost
the race and mkdirs() returned false to signal that it already
existed -- and this was assumed to be a hard failure.

We now recheck existence after a mkdirs() failure to discern this
case and proceed appropriately.

Bug 10515463

Change-Id: I13fbdd838921223f75ab11faa47291c82b21c650