qemu-iotests: Ensure GNU sed is used

Various sed regexp from common.filter use sed GNU extensions.
Instead of spending time to write these regex to be POSIX compliant,
verify the GNU sed is available and use it.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/common.rc

@@ -17,6 +17,19 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+SED=
+for sed in sed gsed; do
+    ($sed --version | grep 'GNU sed') > /dev/null 2>&1
+    if [ "$?" -eq 0 ]; then
+        SED=$sed
+        break
+    fi
+done
+if [ -z "$SED" ]; then
+    echo "$0: GNU sed not found"
+    exit 1
+fi
+
 dd()
 {
    if [ "$HOSTOS" == "Linux" ]