"weave attach $CIDR $CONTAINER_ID" is no longer possible w/o
running weaver. This feature was undocumented and complicated
the weave script, as "weave attach" required to call "create_bridge".
Removing the feature allows us to eliminate the bridge creation
from the script.
Running "weave attach" w/o weaver results in the following err:
bridge "weave" not present; did you launch weave?
Also, this commit simplifies the "attach-container" cmd from
weaveutil by removing "mtu" as a param. The cmd is used
only by "weave attach", and a mtu is value for an attached
container interface is exactly the same as one of the weave bridge.
Martynas Pumputis
541adf6bb1