Error of new-install if default store-dir does not exist

[jneira]

• If store-dir in etlas config file points to a custom directory and the default one in ~\etlas\store\eta-${eta-version}\package.db does not exist, etlas install whatever throws:

  'C:\bin\eta-pkg.exe' exited with an error:
  eta-pkg.exe: C:\Users\user\AppData\Roaming\etlas\store\eta-0.8.4.1\package.db:
  getDirectoryContents: does not exist (El sistema no puede encontrar la ruta
  especificada.)
  )

• With the same config cabal does not throw the error and creates (or uses if already exists) the needed directories in the custom location set in the config file