some syntax error in scenarios section of vitrage-template-format.rst
some syntax error in scenarios section of vitrage-template-format.rst

scenarios should be a list, there are some syntax errors in scenarios section of
vitrage-template-format.rst

Fixes: bug #1585545

Change-Id: I728ace84b98f4ac9a7eaab53a30656e637b3924d
Signed-off-by: dongwenjuan <648f677d6c1326e8822df97fbbc7d15228521866@zte.com.cn>

openstack/vitrage,openstack/vitrage,openstack/vitrage