Make client tests faster

[naved001]

Made some changes in the client tests so that they are faster:

• use null auth backend for most tests
• use initial_db() fixture rather than using populate server

In travis, the client tests were taking around 190 seconds to run, now it runs in like 100 seconds.

[naved001]

I am actually not sure why we didn't we use the initial_db fixture in the first place. Couldn't find it in #617 (there are too many comments to sort through, and github is crashing when loading a page with that many comments).

[naved001]

@Izhmash Addressed your comments, and fixed some more typos that I found.

[zenhack]

This looks basically reasonable to me.

I agree re: initial_db; There was a lot in that PR that I was really annoyed with at the time, and merging it was much more of a quality compromise than I'm normally willing to make.

[naved001]

should we get the user tests to use mock authentication too?

I explained this in person but for posterity, the reason we can't use mock auth for Test_user is because that class is actually testing the calls specific to the database auth backend (creating users, deleting users etc).

[zenhack]

Ack, looking at the merge conflicts now and I'm realizing I didn't think this through. There's a big problem with using initial_db vs. the code that I'm wrote in #1007; none of the obmd_uris in initial_db are actually functional, and they need to be for the integration tests.

[naved001]

Hmmm, you coud use the additional_db fixture (which you can modify to have valid obmd parameters). Or maybe just register a new node or two with valid details just for testing obm calls.

[zenhack]

Ended up doing the latter; I've merged master back in on my branch. Will set about getting the cli tests to pass again.