Yaml tests: Only allow forced continuations on SELECT queries

[ohadzeliger]

The YAML tests are forcing continuations on every query right now. This runs into issues where the underlying implementation does not support setting maxRows. This change prevents forced continuations from taking place in any query but SELECT.
Queries such as UPDATE will not reject a maxRows but will ignore it (returning all rows) which will cause a test to fail validation when the rows returned are validated.
Notes:

• All queries (UDPATE, INSERT, DROP etc) will now execute in "regular" mode even when forced continuation is taking place for SELECTs
• Most data modification is taking place in the setup blocks, and no validation is done, however, this will impact the way that these queries behave as well
• This change assumes that SELECT query begins with "select" string, a more elaborate test can be added later