test/common: Make sure that extdebug is enabled as soon as possible

if given script, which executes under the debug tracer, fails before
xtrace_restore() is called, the BASH_ARGC[] will miss all the arguments
which were passed down till that very point. Similar case can be
experienced after tracer is disabled as then all the arguments hold by
BASH_ARG{C,V}[] become unavailable (i.e. until tracer is enabled again).

Since there's no actual benefit from toggling the extdebug (in fact, it
could break DEBUG|RETURN traps if ever used), enable it once when
autotest_common.sh is sourced and keep it enabled throughout entire
execution of given script.

Change-Id: I01001ead1570967a2e550d993f85f12b9f62553e
Signed-off-by: Michal Berger <michalx.berger@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/477
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

test/common/autotest_common.sh

@@ -5,7 +5,6 @@ function xtrace_disable() {
 			XTRACE_DISABLED="yes"
 		fi
 		set +x
-		shopt -u extdebug
         elif [ -z $XTRACE_NESTING_LEVEL ]; then
                 XTRACE_NESTING_LEVEL=1
         else
@@ -31,7 +30,7 @@ function xtrace_enable() {
 alias xtrace_restore=\
 'if [ -z $XTRACE_NESTING_LEVEL ]; then
         if [[ "$PREV_BASH_OPTS" == *"x"* ]]; then
-		XTRACE_DISABLED="no"; PREV_BASH_OPTS=""; shopt -s extdebug; set -x; xtrace_enable;
+		XTRACE_DISABLED="no"; PREV_BASH_OPTS=""; set -x; xtrace_enable;
 	fi
 else
 	XTRACE_NESTING_LEVEL=$((--XTRACE_NESTING_LEVEL));
@@ -1065,6 +1064,7 @@ function opal_revert_cleanup {
 }
 
 set -o errtrace
+shopt -s extdebug
 trap "trap - ERR; print_backtrace >&2" ERR
 
 PS4=' \t	\$ '