Notify the caller about I/O error

Call onError for caller of BugreportManager.start() if any io error
occurs during runtime.

Bug: 128981582
Test: Tested manually by throwing IO exception in the code when
bugreport is being generated, onError of the callback successfully
called.
Merged-In: I9033d85d392b926041fc26a86806a370752d062d
Change-Id: I9033d85d392b926041fc26a86806a370752d062d