Port coverage API into v3 part2
Port coverage API into v3 part2

This patch contains the changes required to adapt the hypervisor
extension and the corresponding unittest to the v3 framework.

And adding '_import_coverage' for ensure loading coverage module from
python-coverage.

Partially implements bp v3-api-extension-versioning

Change-Id: I6a2dbf00d09132b767cd7972f68cb752b5961796

n0ano/gantt,n0ano/gantt