config: Add -s option to run only specified sections

This commit adds -s option which allows you to specify only certain
sections from the config file to be run. The '-s' argument can be
specified multiple times to allow multiple sections to be run.

The options are still carried between section, that includes the
sections which are not going to be run.

Update README.config-sections as well.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

check

@@ -75,6 +75,7 @@ check options
     -T			output timestamps
     -r			randomize test order
     --large-fs		optimise scratch device for large filesystems
+    -s section		run only specified section from config file
 
 testlist options
     -g group[,group...]	include tests from these groups
@@ -221,7 +222,7 @@ while [ $# -gt 0 ]; do
 			done
 		done
 		;;
-
+	-s)	RUN_SECTION="$RUN_SECTION $2"; shift ;;
 	-l)	diff="diff" ;;
 	-udiff)	diff="$diff -u" ;;
 
@@ -389,6 +390,19 @@ for section in $HOST_OPTIONS_SECTIONS; do
 	OLD_MOUNT_OPTIONS=$MOUNT_OPTIONS
 	get_next_config $section
 
+	# Do we need to run only some sections ?
+	if [ ! -z "$RUN_SECTION" ]; then
+		skip=true
+		for s in $RUN_SECTION; do
+			if [ $section == $s ]; then
+				skip=false
+			fi
+		done
+		if $skip; then
+			continue
+		fi
+	fi
+
 	mkdir -p $RESULT_BASE
 	if [ ! -d $RESULT_BASE ]; then
 		echo "failed to create results directory $RESULT_BASE"