remove hard coded container name when checking if mysl is accepting connection

create.sh

     sleep 1;
 done
 
-while ! docker exec wptest-web /bin/sh -c "mysqladmin ping -h $PREFIX-db -P 3306 --protocol=tcp -u user -puser --silent" ; do
+while ! docker exec $PREFIX-web /bin/sh -c "mysqladmin ping -h $PREFIX-db -P 3306 --protocol=tcp -u user -puser --silent" ; do
     echo "Waiting for the mysql server in the db container to be up and running...";
     sleep 1;
 done