Non-timeout network errors are not fatal when an instance is deleted,
for the same reasons given for removing a haproxy instance in the
prior commit.

It is also not fatal if the admin Secret is missing when we remove
a varnish instance, or when setting its config to the NotReady VCL.
Similar to reasons given for haproxy in prior commits -- in such
cases we assume that Secret has been deleted in an undeployment
operation, so its not necessary to set a "not configured" state,
since the instance will be removed imminently.