Test the `neu update` command a little bit thoroughly

[shalithasuranga]

Right now, we simply check the output of the neu update command. Seems like we can check the functionality with the following steps:

• Update the client/server version in the config to a specific version
• Run neu update
• Test the version with neu version

Assignee @pathange-s

[pathange-s]

Okay, so you mean to check an update to a random version, right? Let me add this test case too.