scripts/nvmf_perf: fix matching result files

When I use a single json config to run 4k and 64k together, the IOPS
for the 4k test were lower than expected because the script is using
metrics from both the 4k_64_randrw_m_100_* and 64k_64_randrw_m_100_*
to calculate the average metrics because 4k_64_randrw_m_100_* is in
64k_64_randrw_m_100_*. Fixed issue by checking, if the result file
startswith the name of the fio config file.

Change-Id: I630385c34223b38694d7e2bb578779627c89866d
Signed-off-by: John Kariuki <John.K.Kariuki@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/10127


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-by: Maciej Wawryk <maciejx.wawryk@intel.com>