shortlog.sh: Improve formatting
shortlog.sh: Improve formatting

Improve the format of the generated shortlog:
- quote the LOG variable to ensure that the whitespace will be
  preserved;
- add more empty lines to visually separate layer reports;
- print the layer name, not its full path.

Pelagicore/vagrant-cookbook,Pelagicore/vagrant-cookbook,Pelagicore/vagrant-cookbook