Some fixes for postgres module

* use password through PGPASSFILE file
* fix checking maintenance_db and runas params: '' and None is equal
* fix bug with escaping in psql_query(), hope default delemiter and quote is enough
* psql_query() now returns list instead of dict, just according table nature
* add gathering tablespace parameter of databases in db_list()
* remove `locale` argument of db_create(), which is probably obsolete
* add db_alter() function for changing db parameters
* present() state now tries to fix db params if it's needed and possible
  (what we disscussed in issue #4164)
* fix pep8, formatting and double quotes