bench: Add fail-fast error path to inodeop_bench

If one of the repeated operations specified by a command fails, report
the error to the user and don't export its metric.

Test: Manual run on physical device
Bug: 165903680
Signed-off-by: Stefano Duo <stefanoduo@google.com>
Change-Id: I3a8caeb6d878b004d89e425bc166c8505fda938a