Git requires network access for all builds

[gonuke]

Describe the Bug

Current build process enforces network access via git submodule

To Reproduce

When building DAGMC, CMake either calls git submodule or checks to see that the (PyNE) submodule is initialized. If neither works then it won't build.

Expected Behavior

Since PyNE is the only submodule and we only need it when building with UWUW, these checks should be localized to that condition.