Keep existing data when moving to containerized MariaDB

Keep existing data when moving to containerized MariaDB

We used named Docker volume for MariaDB storage, which meant that when
moving from BM to containerized wit MariaDB, we lost data and
reinitialized the storage from scratch.

With this commit we keep the data by mounting the original data into the
container.

We also need to make sure that file ownership is correct according to
the MariaDB container image used, and that Kolla bootstrap mechanisms
aren't retriggered, as they aren't idempotent.

Change-Id: I1fc955021c6dd83f1a366495dd8c7281fb9e7cc5