Added pymysql in python2

Change-Id: I5a086bc371286c8f1f51472a4ba2853d17a9abb7

slave-scripts/gate-sahara.sh

@@ -42,14 +42,17 @@ case $plugin in
 esac
 
 pip_cmd="install -U -c https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt -r requirements.txt . --no-cache-dir"
+pip_packages="pymysql"
 
 case $(echo $JOB_NAME | awk -F '-' '{ print $NF }') in
     python3)
        sudo apt install python3-pip python3-dev -y
        sudo pip3 $pip_cmd
+       sudo pip3 install $pip_packages
        ;;
     *)
        sudo pip $pip_cmd
+       sudo pip install $pip_packages
        ;;
 esac