getProcessAgeMs: better error messages am: d9ebe7cef5 am: 9ec25af215 am: 8b4cdbb620 am: 0931811af6

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/1459346

Change-Id: I12ff3f04d1a67f0d6c3879fa1920315be2999e3e