Allow paths that contain symlinks for cachedir

[castulo]

When the path provided by a user for the --statedir (or --cachedir) contains a symlink swupd will fail to extrar tar files since libarchive does not support extracting files through symlinks.

This commit fixes the issue allowing users to use symlinks in the --statediri/--cachedir path.

Closes #1581

Signed-off-by: Castulo Martinez castulo.martinez@intel.com

[castulo]

V2: returning immediately if realpath fails to get the path where a tar is going to be extracted to.

[castulo]

V3:

• checking for the realpath when setting the global statedir variable.