scripts/perf: Update results parsing in nvmf benchmark scripts

Wrong indent level caused results to be duplicated in final
output file if configuration file was used to run more than one
workload combination.

Change-Id: I0fadc10eba38898df648ec2da5fbd0440a3b9693
Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/449150


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Pawel Kaminski <pawelx.kaminski@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>