Changing QST channel password via API throws error

[mmuller]

Nuntium API version 0.21

We received a lot of New Relic alerts for errors occurring in Nuntium (11/24/2015).
In that case the channel was created by Resourcemap staging application through Nuntium API.

[ggiraldez]

When updating a QST server channel and sending the password as part of the configuration options, the server doesn't re-encrypt it and it doesn't calculate a salt. The error is due to the missing salt.

See https://github.com/instedd/nuntium/blob/master/app/models/qst/server/qst_server_channel.rb#L74 and https://github.com/instedd/nuntium/blob/master/app/models/channel.rb#L362