base-files: Check for /run and /var/lock softlinks on upgrade

Commit ea647cd9eebdc3e3121b84074519c4bb305adac9 moved the locations
of /run and /var/lock to match the FHS 3 draft specifications.
However, the install doesn't remove the existing directories.
As a result, upgrading a system may result in /run as a softlink
to /var/run and /var/run as a softlink to /run, creating a circular
link.

During pre-install, check for the existence of the old softlinks and
remove them so the new directories can be installed.

Signed-off-by: Bryan Evenson <bevenson@melinkcorp.com>