metricsd binder: Abort if fail to register service

Assert abort metricsd if binder service registration fails.

If the addService() call fails (for reasons that at least include an SELinux
policy denial), the call to joinThreadPool() apparently processes a stale
pending weak dereference that triggers an abort on a probable double-free:

 F libc    : Invalid address 0xbe8bfa30 passed to free: value not allocated
 F libc    : Fatal signal 6 (SIGABRT), code -6 in tid 609 (metricsd)

Since metricsd is severely hobbled if registration fails, abort and see if
things work better the next time.  If not, the crash loop will hopefully
attract attention to the problem.

Change-Id: I520d0eafb9cb25ee225d589bfd87df4e51f6b181