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.