create-container: allow execution outside of uturn directory

If user executes ./uturn/create-container.sh install ..., then
the script would fail when trying to install the extra uturn
scripts into the container since it looked for them in the
PWD.

This change makes the script find the directory where it lives
and then uses that to determine where the extra uturn scripts are.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>