Use Drizzle JDBC for monasca-thresh in devstack

MySQL Connector is released under GPLv2 license which restricts the
distribution of the consuming project [1]. This change configures
monasca-thresh to use Drizzle JDBC (BSD license) in devstack.

[1] https://governance.openstack.org/tc/reference/licensing.html

Story: 2001522
Task: 6323
Change-Id: I1154e166e1aa6fe6693bdd169d2e5544719fbe6c

devstack/files/monasca-thresh/thresh-config.yml

@@ -109,7 +109,7 @@ sporadicMetricNamespaces:
 
 database:
   driverClass: %MONASCA_THRESH_DATABASE_ENGINE%
-  url: "jdbc:mysql://%DATABASE_HOST%:%DATABASE_PORT%/mon?useSSL=true"
+  url: "jdbc:drizzle://%DATABASE_HOST%:%DATABASE_PORT%/mon"
   user: "%DATABASE_USER%"
   password: "%DATABASE_PASSWORD%"
   properties:

devstack/plugin.sh

@@ -968,7 +968,7 @@ function install_monasca_thresh {
 
     sudo chmod 0640 /etc/monasca/thresh-config.yml
 
-    local dbEngine="com.mysql.jdbc.jdbc2.optional.MysqlDataSource"
+    local dbEngine="org.drizzle.jdbc.DrizzleDriver"
     local dbPort=3306
 
     if [[ ${MONASCA_DATABASE_USE_ORM} == "True" ]]; then