Testing: Test of restart code needed

[prckent]

Clear tests (and therefore examples) of working restarts with VMC and DMC are needed.

Based on these tests, the restart code can be updated/cleaned/rewritten as needed. No need for backward compatibility.

[prckent]

@markdewing Delegate/ask for helpers as needed

[prckent]

This is also needed to interface with the ECP VeloC project.

[ye-luo]

This part of my project for the summer student. Deal with the restart and paralell IO.

[prckent]

Tests are due by end of June. Fixes later.

[prckent]

Provisionally added as a requirement to the next release (3.1) particularly in light of bug referenced in #2 . Would prefer to have fixed unless it looks to be overly complicated.

[ye-luo]

I have prepared the test case for checking restart. Not integrated into ctest yet.
The electron coordinates and random numbers seem loaded correctly.

1. The extra VMC block (no electron move) and the restart run with the same VMC block agree on KE, ElecElec, LocalECP but NonLocalECP is slightly different. I can't trace all the places where random numbers are used.
2. Run the restart run many times and I got exactly the same results even the initial random seed is not fixed.

So I will set up the checking based on the energy components except NonLocalECP.

[prckent]

I'll close this since the VMC restart tests are incorporated ( #249 ). DMC restart currently also looks clean ( #267 ) so we'll need a specific reproducer/bug report with inputs to make progress, if still needed.