[entropy.tools] dump_entropy_metadata: follow symlinks when determining file size

The package file passed as input might be pointing to a symlink.
If we use lstat().st_size we will get the symlink file size back
rather than the source file size, which is of course unwanted.

This is part of the fixes for bug 4604.
[entropy.client.package] Do not alter repository package file directory permissions

It was observed that the new locking mechanism introduced a problem
with the management of repository package files (.tbz2 files passed
to "equo install", for instance). Try to avoid that by symlinking
the package file to a safe location and using this one as pkgpath.

This fixes bug 4604.