Add a store test for registering a name that was revoked

[Leo Arias]

The store added a new error code for when a user tries to register a name that he previously registered but is now revoked.

We should add an integration test to test the error message returned in this case.

[Leo Arias (elopio)]

Currently, the error code returned by the store is 'already_owned'. Matias will split it in a new error code, called 'revoked_name', so we can show different errors for those two conditions in an easier way.

[Leo Arias (elopio)]

MP for the new code in the store already proposed:
https://code.launchpad.net/~matiasb/software-center-agent/revoked-name-error-code/+merge/334827

[Leo Arias (elopio)]

sergiusens | matiasb elopio nessita we could switch to using the messages from the store, I think register is still based on the old code
sergiusens | we should probably add a task to look at this

[Leo Arias (elopio)]

TThis is for future work, when we get another review on the store error messages:

elopio | mpt: so, in this case, should the error message tell the user to send an email if she thinks the name shouldn't have been revoked? Or maybe point to the revoke reasons? Or just leave it without further explanation?
mpt | elopio, I guess it depends on how likely it is that it’s a mistake. If it’s quite likely, put the instruction in the error message. If it’s unlikely, delegate the instruction to the page listing the revocation reasons.
elopio | I think it's pretty unlikely that somebody revoked something by mistake.
elopio | matiasb: is it possible for the store to send us the reasons?
matiasb | elopio, it should be possible, I think
matiasb | I mean, a reviewer revoking the name must provide a comment, we should be able to include this information in the response; in any case, the developer should have got an email about it too, at that time