cinder db migration to version 127 fails on centos7

[Akihiro Motoki]

neutron-vpnaas has a CentOS 7 gate check, but cinder db migration 126 -> 127 fails with an error "Specified key was too long; max key length is 767 bytes"

ERROR oslo_db.sqlalchemy.exc_filters [-] DBAPIError exception wrapped from (pymysql.err.InternalError) (1071, u'Specified key was too long; max key length is 767 bytes') [SQL: u'\nALTER TABLE quota_usages CHANGE COLUMN resource resource VARCHAR(300)'] (Background on this error at: http://sqlalche.me/e/2j85): InternalError: (1071, u'Specified key was too long; max key length is 767 bytes')

http://logs.openstack.org/41/625441/2/check/neutron-vpnaas-tempest-libreswan-centos/82fc69f/job-output.txt.gz#_2018-12-16_18_27_56_495315

(The above log is also copied to http://paste.openstack.org/show/737449/)

neutron-vpnaas job configuration is found at [1] and we use devstack-single-node-centos-7 as a testing node.

[1] https://github.com/openstack/neutron-vpnaas/blob/96f3f4d9731851b61b4ccb1a50ffcafd5cde5624/.zuul.yaml#L47-L61

[LIU Yulong (dragon889)]

Mark as duplicate since a former reported bug.