The bridge-utils package has been deprecated for some time now [1] and
'brctl' does not exist on some more recent distros like Fedora 28.
Replace references to brctl with the proper ip commands.
Calls to "brctl show" are not being replaced with calls to "bridge link"
because the output format is very different and in testing some bridges
were not listed. So the simpler method of consulting /sys/class/net is
used.
In worlddump.py we try running both because failures are handled
gracefully by _dump_cmd(), as well as "ip link show type bridge" for
additional info.
[1] https://lwn.net/Articles/703776/ for example
Change-Id: Ie4c8ad6ce4a09c38023c9e4ec7834c249403145f
Partial-Bug: #1801919
56946cfc5f