Update gcloud.storage docs to use 'from gcloud import storage'

[jgeewax]

Looks like we use import gcloud.storage a lot in the storage docs (http://googlecloudplatform.github.io/gcloud-python/latest/storage-api.html).

I'd prefer if we kept it consistent with datastore, to use from gcloud import storage.

Thoughts?

[dhermes]

I do too. Much to be done still in docs storage (see #632)

[dhermes]

Running

$ git grep 'import gcloud\.storage'

turns up nothing while

$ git grep 'from gcloud import storage' | wc
     10      51     562