WIP: deis-store-volume component - mount RBD images; share volumes across hosts/components

This introduces **deis-store-volume** as a new component which runs on all hosts - it is a global fleet unit. Its purpose is to create, format, and mount an RBD image at /data. This volume is intended to be used by the `controller` and `logger` components - currently they require being on the same host and sharing volumes with `logger-data`, but that's something we want to remove as part of #985.

This is not yet ready to merge and is rough around the edges, but @pierrekircher asked for some code. This was previously blocked as described in #2041, but I found a way to get RBD volume mounting within containers to work.

Currently, it doesn't look like /data on the host is being populated, but it is within the store-volume container. There also seems to be a lag when creating files on one host and viewing them on the other. We'll need to investigate if this is a feasible implementation for controller/logger log sharing.

**To-Dos**
- [ ] Fix bugs
- [ ] Ensure controller and logger work properly when using /data
- [ ] Update store tests
- [ ] Update store documentation

closes #2041
closes #985