Tests in PostgreSQLValueMetaBaseTest are not specific to PostgreSQL

Some database test is generic and should be moved away of PostgreSQL database plugin:

• testMetdataPreviewSqlSmallIntToPentahoInteger

Only keep test specific to PostgreSQL like

• testMetdataPreviewSqlDoubleWithTooBigLengthAndPrecisionUsingPostgesSQL

And some test come from value meta:

• testGetTrimTypeCode()
• testIsNumeric())