it used to only contain service, and used the same string for the bridge. This
is not flexible enough to run off-the-shelf unikernels (configured for bridge
"service" and "management" on multi-homed servers). The old behaviour is the
new default (i.e. "--net=service" creates and attaches a tap device to bridge
"service", and passes "--net:service=tapYY" to the solo5 tender). But it is more
flexible now: "--net=service:other-bridge" will create a tap device attached to
"other-bridge" and pass "--net:service=tapYY" to the tender. This way, there's
no need to match bridge names on the actual server with network device names of
the unikernels.
NB: this is (mostly) backwards-compatible: the on-disk data structures are
versioned (and the version is bumped with this PR), an old albatross client can
send "create" commands to a new server. But a new client will get a parse error
from an old server - which is fine taking into consideration the deployment
base.
