optional pymysql support

This allows you to specify MYSQL_DRIVER=PyMySQL and get it in the
environment.

Change-Id: Ic9d75266640b7aa6d7efb6e882d3027e81414059

files/venv-requirements.txt

@@ -1,7 +1,6 @@
 # Once we can prebuild wheels before a devstack run, uncomment the skipped libraries
 cryptography
 # lxml # still install from from packages
-MySQL-python
 # netifaces # still install from packages
 #numpy    # slowest wheel by far, stop building until we are actually using the output
 posix-ipc

lib/databases/mysql

@@ -11,6 +11,13 @@
 MY_XTRACE=$(set +o | grep xtrace)
 set +o xtrace
 
+MYSQL_DRIVER=${MYSQL_DRIVER:-MySQL-python}
+# Force over to pymysql driver by default if we are using it.
+if is_service_enabled mysql; then
+    if [[ "$MYSQL_DRIVER" == "PyMySQL" ]]; then
+        SQLALCHEMY_DATABASE_DRIVER=${SQLALCHEMY_DATABASE_DRIVER:-"pymysql"}
+    fi
+fi
 
 register_database mysql
 
@@ -155,8 +162,10 @@ EOF
 
 function install_database_python_mysql {
     # Install Python client module
-    pip_install_gr MySQL-python
-    ADDITIONAL_VENV_PACKAGES+=",MySQL-python"
+    pip_install_gr $MYSQL_DRIVER
+    if [[ "$MYSQL_DRIVER" == "MySQL-python" ]]; then
+        ADDITIONAL_VENV_PACKAGES+=",MySQL-python"
+    fi
 }
 
 function database_connection_url_mysql {