scripts/simplebench improvements for 2021-05-04

# gpg: Signature made Tue 04 May 2021 09:45:15 BST
# gpg:                using RSA key 8B9C26CDB2FD147C880E86A1561F24C1F19F79FB
# gpg: Good signature from "Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 8B9C 26CD B2FD 147C 880E  86A1 561F 24C1 F19F 79FB

* remotes/vsementsov/tags/pull-simplebench-2021-05-04:
  MAINTAINERS: update Benchmark util: add git tree
  simplebench/bench-backup: add --drop-caches argument
  simplebench/bench-backup: add --count and --no-initial-run
  simplebench/bench-backup: support qcow2 source files
  simplebench/bench_block_job: handle error in BLOCK_JOB_COMPLETED
  simplebench/bench-backup: add target-cache argument
  simplebench/bench-backup: add --compressed option
  simplebench: bench_one(): support count=1
  simplebench: bench_one(): add slow_limit argument

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>