the wavefunction xml file does not carry the full path of vp.h5

**Is your feature request related to a problem? Please describe.**
when optimizing a parameter (regardless of the parameter), a vp.h5 file is created and a reference to the *.s0*.vp.h5 is added to the opt.xml file. In case were the wavefunction definition (XML definition) is in a stand alone file called from a qmc.in.xml file, the route is just to overwrite the wfj.xml file and replace it with the best opt.xml file. However, the opt.xml now carries the call to the vp.h5 file and the global path is not indicated. The solution to avoid the code of crashing is to either delete the line or correct it by adding the absolute path.

**Describe the solution you'd like**
- The vp.h5 file path is an absolute path.
- The vp.h5 line is only added with a flag in the optimizer "vp.h5=true"

**Additional context**
This is an issue for automated runs where script replace the wfj.xml file with opt.xml file