fix --excluded of meter-label-rule-create is not working

rule['excluded'] is boolean type, should not be compared with 'true'

Closes-Bug: #1248002
Change-Id: Ie78c307ede1f7124c58354825a411474ff6c1234
(cherry picked from commit 504f496d6b4fd6234c3e65ba636ee12b004fae1f)
Merge "fix --excluded of meter-label-rule-create is not working" into stable/havana
Merge branch 'stable/havana' of https://github.com/openstack/quantum into havana/stable