In Nomad 0.9, we made volume driver handling the same for `""`, and
`"local"` volumes. Prior to Nomad 0.9 however these had slightly different
behaviour for relative paths and named volumes.
Prior to 0.9 the empty string would expand relative paths within the task
dir, and `"local"` volumes that are not absolute paths would be treated
as docker named volumes.
This commit reverts to the previous behaviour as follows:
| Nomad Version | Driver | Volume Spec | Behaviour |
|-------------------------------------------------------------------------
| all | "" | testing:/testing | allocdir/testing |
| 0.8.7 | "local" | testing:/testing | "testing" as named volume |
| 0.9.0 | "local" | testing:/testing | allocdir/testing |
| 0.9.1 | "local" | testing:/testing | "testing" as named volume |
a096a7f112