tox in Tryton: setenv

Some environment variables for the database

setenv =
  sqlite: TRYTOND_DATABASE_URI={env:SQLITE_URI:sqlite://}
  postgresql: TRYTOND_DATABASE_URI={env:POSTGRESQL_URI:postgresql://}
  mysql: TRYTOND_DATABASE_URI={env:MYSQL_URI:mysql://}
  sqlite: DB_NAME={env:SQLITE_NAME::memory:}
  postgresql: DB_NAME={env:POSTGRESQL_NAME:test}
  mysql: DB_NAME={env:MYSQL_NAME:test}