Revert "UCLOUDNG-534: do not allow multi-nic or user defined network"

This reverts commit 4c2fb71d2ac6c9f8c1b7b30b5ecad70c8d418e5b.
Revert "Fix unit test to work with pre-defined network"

This reverts commit d638da5b88956816f4f2a7c650871fa09bbe0bd5.