Fix location for coverage reports
Fix location for coverage reports

The gate job expects the report to exist under
the "cover" directory by default, and not "reports".

[1] https://git.io/fAfx9

Change-Id: Iadbedcca91f4a9e8a12b3d3b2026af37ff4d0b21

openstack/manila-ui,openstack/manila-ui,openstack/manila-ui