Enable multiple concurrent binderLibTest instances

Each instance tries to register a service with the
same name, so suffix the service name with the
instance's PID to avoid collisions.

Test: Tests run and pass in 2 processes at once
Change-Id: I685b01fbfbad4e9bd3eb6ea06f46ffc157169909
Signed-off-by: Connor O'Brien <connoro@google.com>