ServiceStartTimeout is defined at e2e core framework and the one of
the core is used at many places, but the one of this endpoints/ports.go
is not used at the other places.
So this removes the one of endpoints/ports.go for the cleanup.
WaitForEndpoint() of the endpoints e2e framework was used in
test/e2e/network/proxy.go only. In addition, the endpoints e2e
framework imported the core of e2e framework only for the function.
So this moves the function into test/e2e/network/proxy.go then we
can remove dependency of core framework from the sub e2e framework.
