cinder-type: delete PATH in exec

By deleting PATH, we are able to run both commands (cinder type-* and
grep) without environment issue.

Change-Id: I5dd1c60892c7848b02ab71ea30bc49b4b4c26029
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
(cherry picked from commit 6e052620481055cffced7911a0f31bfd0849c68a)