make spm cache_dir instead of all cachedirs

This will allow spm to be run as a non root user, with a cache dir set to
somewhere other than /var/cache/salt.

salt/cli/spm.py

@@ -30,7 +30,7 @@ class SPM(parsers.SPMParser):
         self.parse_args()
         self.setup_logfile_logger()
         v_dirs = [
-            self.config['cachedir'],
+            self.config['spm_cache_dir'],
         ]
         verify_env(v_dirs,
                    self.config['user'],