BUGFIX - slight typo in format for  message when trying to symlink

Was resulting in a stack dump due to the formatted string missing
the correct parameter.
BUGFIX: Importing wrong arch results in silent error

Self explanatory. If you import --arch=invalid, a bug in
manage_import_redhat.py goes down a path that uses the string
module without importing it, resulting in a wierd error to
stdout/stderr which gives no clue what the problem is - and a
not super easy to track down error to the log. This trivial
patch fixes this.