Cloud Spanner client incorrectly handles NOT_FOUND error returned by create database

[vkedia]

While creating a database, is the backend returns NOT_FOUND error, the client assumes it to indicate that instance is not found and thus returns "Instance not found" error message:
https://github.com/GoogleCloudPlatform/google-cloud-python/blob/master/spanner/google/cloud/spanner_v1/database.py#L213

This is not always the case as cloud spanner can return NOT_FOUND in other scenarios. For eg in the "CREATE INDEX ... " ddl statement that table that the index is being created on does not exist it would return a NOT_FOUND. I think the fix would be to just pass the error message returned by the rpc to the user.

This can be reproduced using:

from google.cloud import spanner

"""Creates a database and tables for pattern 1 sample data."""

spanner_client = spanner.Client()

instance = spanner_client.instance("test-instance")



database = instance.database("bitemporal_pattern1", ddl_statements=[

    """CREATE TABLE MyTable (

        Id        String(36) NOT NULL,

        Field1  STRING(36) NOT NULL

) PRIMARY KEY (Id)"""

,

"""CREATE INDEX IDX ON yTable (Field1)"""

])



operation = database.create()



print('Waiting for operation to complete...')

operation.result()

[vkedia]

@lukesneeringer @tseaver Any updates on this?