Add Cloud Spanner dialect support

Example events-log.config update:

[events-log]
    storeDriver = com.google.cloud.spanner.jdbc.JdbcDriver
    storeUrl = jdbc:cloudspanner:/projects/project-name/instances/instance-name/databases/db-name

As the Spanner jdbc driver does not allow allowMultiQueries it
was necessary to add a Spanner-specific case in index creation.

Spanner does not support AUTOINCREMENT and recommends against
implementing it as it creates hotspots, so we use GENERATE_UUID()
for primary key creation:
https://cloud.google.com/spanner/docs/schema-and-data-model#choosing_a_primary_key

Change-Id: I7c9ead0ff59af681c13d753f13a19e36cc44dd0c
4 files changed