Flakiness in raft_consensus-itest due to no process to resume

Commit 86116e4 has surfaced a source of flakiness in raft_consensus-itest where there's no process to resume.

adar reported 3 failures in 1000 run with messages like:

Check failed: _s.ok() Bad status: Illegal state: Request to resume '/tmp/run_tha_testp3dlYu/build/debug/bin/kudu-tserver' but the process is not there

The link for the flakiness stats of the raft_consensus-itest:
http://dist-test.cloudera.org:8080/test_drilldown?test_name=raft_consensus-itest