SlaterDetBuilder I/O issues

[ye-luo]

Not necessarily bugs but a few things need to be better handled in https://github.com/QMCPACK/qmcpack/blob/develop/src/QMCWaveFunctions/Fermion/SlaterDetBuilder.cpp

• error output handling. app_abort should be avoided.
• avoid repetitive I/O in readDetListH5. Better to read by one rank and then bcast.

[prckent]

Fair points. Reading and bcasting probably most impactful. I would add (3) Repeated code and (4) Lack of input validation as well. It is very trusting of the input. However it does work for present day-to-day purposes.