test/common: Add xtrace_disable_per_cmd()

This function is an alternative to xtrace_disable() which works
within a smaller scope, i.e., per cmd. Useful to quickly hide
verbose output without disabling entire tracing.

Signed-off-by: Michal Berger <michal.berger@intel.com>
Change-Id: I284eafaf0e74764f329a7a6897a7d7fa85176de7
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16363
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: John Kariuki <John.K.Kariuki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

test/common/autotest_common.sh

@@ -29,6 +29,8 @@ function xtrace_disable() {
 	fi
 }
 
+function xtrace_disable_per_cmd() { eval "$* ${BASH_XTRACEFD}> /dev/null"; }
+
 xtrace_disable
 set -e
 shopt -s expand_aliases