Provide multiple versions of Airflow

[guangie88]

Currently there are different builds for Spark-1.6 and Spark-2.1 (due to datagovsg use case), but not for Airflow itself, which is kind of strange since this is an Airflow repository.

Considering there is at least one major differences between v1.9 and v1.10, such as the setting of system timezone (https://issues.apache.org/jira/browse/AIRFLOW-288), there should be various builds to build different Airflow versions.

Would be ideal to pair up with various Spark version builds, but at the same time try not to overly complicate the number of combinations of components.