system-test: avoid awkward cell.name values

A few of the system-test cell.name values includes a forward
slash character, which the cells shell interprets as an
attempt to switch to the alternative addressing mode.

This patch updates these cells to use the neutral '-' character
instead.

Patch: http://rb.dcache.org/r/5585/
Acked-by: Gerd Behrmann
Target: master
Request: 2.6