Binder: Be forceful about a forceful exit.

We were previously using exit(1) when code servicing an IPC threw
any subclass of Error. That made it much harder to diagnose cases
where that happened because :

- exit runs global destructors, which might prove problematic (see
  linked bug).
- such exits are often due to bugs in application code (things like
  AssertionErrors being thrown) but aren't flagged as such by our
  infrastructure, or by humans for that matter.

To address both issues, use FatalError() so that the runtime can dump
more useful information to the logs before it aborts.

Test: manual
Bug: 36813403
Change-Id: I5826090229109dc7cb19f0c3571c609f990cd36a