change docker file to use private repo for db2express-c
change docker file to use private repo for db2express-c

Dockerfile referred to a public repo of db2express-c this is not
available any more.  Changed to refer to the private repo.  Access to
this repo available on request from the owners.  See the README for
details

Anthonyo2015/bfdocker,bigfix/bfdocker,Anthonyo2015/bfdocker,Anthonyo2015/bfdocker