Improve bulk symlink error handling
Improve bulk symlink error handling

If the tempdir doesn't exist, we can get a cryptic error message when
using the bulk_symlink function. This change checks that the temp dir we
are to use exists prior to consuming it and throws a message indicating
the folder doesn't exist.

Change-Id: I3a4bf279d6d1c2c35c000e7b38b147a026cfcfb4
Closes-Bug: #1804527

openstack/python-tripleoclient