BigQuery: Add support to Dataset for project_ids with org prefix.

[ryanreno]

Similar to #7827. Can not create a Dataset using a project ID with org prefix.

Environment details

1. Python version: Python 3.6.5
2. google-cloud- version:
   Name: google-cloud-bigquery
   Version: 1.16.0

Steps to reproduce

1. Follow the Creating a Dataset guide

Code example

from google.cloud import bigquery

client = bigquery.Client()

dataset_id = f"{client.project}.ryan_dataset".

# Construct a full Dataset object to send to the API.
dataset = bigquery.Dataset(dataset_id)

Stack trace

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-14-bfe46d108801> in <module>
----> 1 dataset = bigquery.Dataset(dataset_id)

~/.virtualenvs/bigquery/lib/python3.6/site-packages/google/cloud/bigquery/dataset.py in __init__(self, dataset_ref)
    368     def __init__(self, dataset_ref):
    369         if isinstance(dataset_ref, six.string_types):
--> 370             dataset_ref = DatasetReference.from_string(dataset_ref)
    371         self._properties = {"datasetReference": dataset_ref.to_api_repr(), "labels": {}}
    372 

~/.virtualenvs/bigquery/lib/python3.6/site-packages/google/cloud/bigquery/dataset.py in from_string(cls, dataset_id, default_project)
    305                 "Too many parts in dataset_id. Expected a fully-qualified "
    306                 "dataset ID in standard SQL format. e.g. "
--> 307                 '"project.dataset_id", got {}'.format(dataset_id)
    308             )
    309 

ValueError: Too many parts in dataset_id. Expected a fully-qualified dataset ID in standard SQL format. e.g. "project.dataset_id", got google.com:[project].ryan_dataset

I removed the project name from the stack trace.

[ryanreno]

A workaround I found:

from google.cloud import bigquery

client = bigquery.Client()

dataset_id = 'ryan_dataset'
dataset_ref = bigquery.DatasetReference.from_string(dataset_id, default_project=client.project)

dataset = bigquery.Dataset(dataset_ref)
dataset.location = 'US'
dataset = client.create_dataset(dataset)