added a script to copy initial storage settings into volume

in order to persist /opt/graphite/storage between container restarts, we need to take steps to 

1. setup default /opt/graphite/storage settings files etc (pip adds a bunch of stuff)
2. backup to /opt/graphite/storage.bak
3. allow docker to create the data volume  /opt/graphite/storage on the host 
4. copy the initial files back, if they don't exist already