tests: fix tests according the new behavior of vle

Sources and binaries of packages are now separated. The test process
based on the compilation of packages had to be updated.
fix: unload library and warnings

- on unload, the rvle library was not unloaded.
- old functions were still used.
- man pages have been updated, taking into account the fact that vle
  does not have PRNG
fix: inputs as dataframe

- Run call of simulation of inputs given as data frame leads to an error
  when restoring the previous inputs.
- Documentation of Rvle class has been updated with an example of using
  inputs as data frames.
fix: management of null outputs

When simulating plans, if for example output plugin of view is not
declared as storage, the null output was not taken into account.