Update after switching one 1n-tx2 and the idle ThunderX2 servers between
racks. Update the idle ThunderX2 specs to a new perf testbed, 2n-tx2.
Add Server-Type-B12 which is a modified Server-Type-B2 with one extra
NIC (needed for 2n-tx2).
Change-Id: I51af358f1feb476652eddfe82b5af1d0d70ac259 Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>