db_url_config does not handle all postgres urls the same

[sww314]

In particular, if you are trying to use a Cloud SQL Connection string and use POSTGIS as the engine it sets the database name as the host name.

If you are running on Google Cloud Run and want to connect to Google Cloud SQL instance with postgis, this will fail.

In [11]: POSTGRES = "postgres://user:password@//cloudsql/project-1234:us-central1:instance/dbname"                              

In [12]: POSTGIS = "postgis://user:password@//cloudsql/project-1234:us-central1:instance/dbname"                                

In [13]: Env.db_url_config(POSTGIS)                                                                                             
Out[13]: 
{'NAME': '/cloudsql/project-1234:us-central1:instance/dbname',
 'USER': 'user',
 'PASSWORD': 'password',
 'HOST': '',
 'PORT': '',
 'ENGINE': 'django.contrib.gis.db.backends.postgis'}

In [14]: Env.db_url_config(POSTGRES)                                                                                            
Out[14]: 
{'NAME': 'dbname',
 'USER': 'user',
 'PASSWORD': 'password',
 'HOST': '/cloudsql/project-1234:us-central1:instance',
 'PORT': '',
 'ENGINE': 'django.db.backends.postgresql'}

[sergeyklay]

This is resolved in develop branch. Thank you for the report, and for helping us make django-environ better. And I am sorry about the delay.