Add Mercurial support to TribitsCTestDriveCore.cmake

[lefebvre]

This issue is for adding mercurial support into native TriBITS cmake.
Initial scope is the ctest/TribitsCTestDriverCore.cmake, which supports git and svn.
Ross can elaborate on further version control usage which will also be addressed by this issue.

[bartlettroscoe]

Jordan, to make this more exact, I will change the title to "Add Mercurial support to TribitsCTestDriveCore.cmake". I think other Github issues should be created for other parts that use version control like generating RepoVersion.txt files. For full version tracking of SCALE which includes the Trilinos and Exnihilo repos that would be useful.

Adding Mercurial support to TribitsCTestDriveCore.cmake should be pretty easy. We can update the unit tests for this too. This is the easiest TriBiTS code for which to add Mecurial support.

However, given that SCALE by itself defines over 150 packages, I don't think you are going to like the way that TribitsCTestDriverCore.cmake handles SCALE. It will reconfigure and rebuild SCALE 150+ times just to get through a single build! I think SCALE should really consider restructuring its package structure to use some higher-level packages and then using subpackages to manage lower-level dependencies. At some point we should discuss how SCALE can better take advantage of TriBITS in this respect.

Also note that SCALE will want to exclude Trilinos packages from SCALE's set of primary meta-project packages (see #9).

[bartlettroscoe]

Given that SCALE at ORNL is moving to git soon, is there any reason to keep this issue open?