Tell rsync to preserve hard links for git objects/packs directories

Without -H option the rsync will sync the files that are hardlinked on
the source side as separate files on receiver side. In some situations
this might make it impossible to restore appliance from backup as
restored repository filesystem contents can be several times bigger
than original contents used to create backup.
Merge remote-tracking branch 'kjedruczyk/rsync-hardlinks'
Remove assumption in test about presence of a git config

The tests listed below run git commit which fails when a git config does not provide user.email.

+ test/test-ghe-backup-repositories-rsync.sh
+ test/test-ghe-restore.sh
+ test/test-ghe-backup.sh
Rename libexec to share/github-backup-utils

sed -i '' -e 's/libexec/share\/github-backup-utils/g' $(git ls-files)
mkdir -p share/github-backup-utils
git mv libexec/* share/github-backup-utils
sed -i '' -e 's|)/\.\.|)/\.\./\.\.|g' $(git ls-files share)
Add debian packaging