nodebuilder/tests/tastor: Teardown logic cleans up network

[renaynay]

teardown leaves network currently, needs to clean up network.

Deleted Networks:
tastora-gxvywoei
tastora-ljrlokqu
tastora-cpxxjffe
tastora-samidpwx
tastora-pkjzezxj
tastora-npdowrsl
tastora-ldisoiqr
tastora-azejdvzl
tastora-szmqtpxw
tastora-mlfqzimr
tastora-tqlcxuwn
tastora-cfeccpyx
tastora-cqlqsdgc
tastora-gxsubmyb
tastora-paavnpbw
tastora-yzzqrgii
tastora-tkihdhdy
tastora-bklfxqwy
tastora-cqmmcmay
tastora-ykwphsbq
tastora-uxyuumsn
tastora-deumtafo
tastora-stnvegxn
tastora-zbivhmkc
tastora-qobwzfun
tastora-bahfqdla
tastora-jzlgywmh
tastora-uagglnsn
tastora-hdpwyxtv