Add avocado dependency to metatdata migrations

This dependency is now automatically added to migrations generated with
the avocado 'migration' command but these migrations were created before
that code was added so the dependencies are being retroactively added to
the migrations here.

Signed-off-by: Don Naegely <naegelyd@gmail.com>
Merge pull request #189 from cbmi/issue-184

Add avocado dependency to metatdata migrations