13937: Fixes file naming inconsistency between storage drivers.

Arvados-DCO-1.1-Signed-off-by: Lucas Di Pentima <ldipentima@veritasgenetics.com>

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/unix_volume.go
similarity index 100%
rename from services/keepstore/volume_unix.go
rename to services/keepstore/unix_volume.go

diff --git a/services/keepstore/volume_unix_test.go b/services/keepstore/unix_volume_test.go
similarity index 100%
rename from services/keepstore/volume_unix_test.go
rename to services/keepstore/unix_volume_test.go