The extend_share is in Manila core, we can support the new API in
the HDFS drivers. This patch adds methods to the driver along with
its unit tests, and updates related docs.
Implements: blueprint hdfs-native-extend-share
Change-Id: Ia81291eda49dc20c3318f71c51d36682d2aae742
Add the hdfs_native driver developer doc with requirements,
supported operations, configurations, and limitations.
Change-Id: Ifbe785f25e779be6871ebc8474f9fbb1d38af82b