Backport of eclipse-vertx#1649

Create a shared rule instance in ContainerPgRule.

This instance is used where we don't need particular customization (SSL, different user, ...etc.).
In ContainerPgRule#after method, we skip stopping the server if the method is called on the SHARED instance.
Therefore, we avoid starting/stopping the PostgreSQL container before/after each test class.
On my box, the builds takes 1-2 minutes instead of 5-6 minutes.
This behavior is aligned with MySQL, MSSQL and Oracle clients testing.

Also, modified EnumeratedTypesExtendedCodecTest#testEncodeEnumArrayEmptyValues.
It checked a column that had nothing to do with enum array.
Without this change, we cannot use a shared rule.

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>