change m1.* flavor to "yardstick-flavor"

change m1.* flavor to "yardstick-flavor"

JIRA: YARDSTICK-485

In OpenStack Newton, the 'm1.tiny', 'm1.small', 'm1.medium' and 'm1.large' will
not be automatic created. This may cause errors as some Yardstick testcases are
using one of these flavor. Therefore, it's better change all the flavor option
in task configuration file to 'yardstick-flavor'.

Change-Id: Ibb29a77ef331bbf728dec9894a2e9f17c19d5ebd
Signed-off-by: JingLu5 <lvjing5@huawei.com>