Allow account changes in cloudml_predict() and cloudml_train()

[javierluraschi]

See #94 - Looks like we can easily switch accounts to support the gcloud parameter.

[jjallaire]

Could we make this a with_account() function which switches back to the previous account after the function completes?

[jjallaire]

Besides saving and restoring this info, we also need to make sure we save and restore all of the gcloud config variables in play (account, project, and region). We also need to make sure that if the user provides a named configuration we read all of the values from the named configuration and set those during the job)

[jjallaire]

We also need to make sure that the gcloud parameter is available in the gs_ family of functions

[javierluraschi]

Alright, let's close this one and I'll remove glcoud and replace with region for cloudml_train.