Add a centos 6 image for building OMERO in multiple environments

Ice 3.3, 3.4, 3.5
Java 1.6, 1.7
Python 2.6, 2.7 (2.7 with Ice still needs to be sorted out)
Merge pull request #9 from manics/omero-build-c6-multienv

Centos 6 image for building OMERO in multiple environments