* Support importing google_sql_user
* Updated documentation to reflect that passwords are not retrieved.
* Added additional documentation detailing use.
* Removed unneeded d.setId() line from GoogleSqlUser Read method.
* Changed an errors.New() call to fmt.Errorf().
* Migrate schemas of existing GoogleSqlUser resources.
* Remove explicitly setting 'id' property
* Added google_sql_user to importability page.
* Changed separator to '/' from '.' and updated tests + debug messages.
