1.keep the column display order consist in extension list with
and without "--long" option.
2.rework for network extentsion list, openstacksdk return object,
so the logic should be same with other service.
3.add some unit test cases, like: extension list --network --long,
extension list --network --compute, to cover regular use cases.
4.raise exact exception when network extension don't exist, avoid
internal TypeError in "extension show" commands.
Change-Id: I2e23ced80d8da8aa1106b22472db850367b351ce
Closes-Bug: #1689233
acc2d106ab