Make an error message more informative

From
https://android-build.googleplex.com/builds/tests/view?testResultId=TR66328435937757440&invocationId=I00700010119503421

:

system/core/init/init_test.cpp:219: Failure
Failed
Value of: service->Start()
  Actual: createProcessGroup(0, 15611) failed for service 'console'
  Expected: is ok

The above error message does not contain enough information to
root-cause the test failure. Hence this CL that makes an error message
more informative.

Bug: 262090304
Change-Id: I09929b2f2aabf1eec4d90ec93234a9e968888da4
Signed-off-by: Bart Van Assche <bvanassche@google.com>