PersistentVolume for gcsfuse mount not being removed on kctf chal stop

[arxenix]

when doing kctf chal stop, the pv for a challenge does not appear to be getting removed.

this subsequently causes kctf chal start to fail,

we've been having to run kubectl delete pv $pv_name after kctf chal stop to get it to work

-- todo: add some logs later, just opening issue for now

[sroettger]

@sirdarckcat

[sirdarckcat]

the persistenvolume should "belong' to the challenge, so if it's not working maybe we forgot to add it as a parent?