Allow to pass options to build.py using BUILD_OPTIONS in OMERO.sh

This commit should solve failing ice34 builds because of javac out of memory
exception. Rather than increasing the default value of the maximum memory in
`build.py`, builds should now pass by setting `BUILD_OPTIONS` to `-Djavac.maxmem=950M`.

To be tested with the OMERO-merge-develop-ice34 build.

/cc @cxallan, @joshmoore, @bpdindelski