skip downloading VMTK test data during build #80
Description
Currently, while building VMTK it downloads the VMTK/tests/vmtk-test-data/ submodule, which contains about 500 MB of test images that we don’t use. This wastes bandwidth, disk space and slows the build process down; let’s change our build scripts (either CemrgApp/CMakeExternals/VMTK.cmake or within our VMTK fork) to skip this.