Remove ast and load using JSON loader

We can use the JSON loader to suck in the backup_lvs array from the
configuration INI file, so we do so.
Signed-off-by: Robert Spencer <rspencer@lbsd.net>

scripts/backstep-traceback-auto

@@ -19,7 +19,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 """
 
 import argparse
-import ast
 import configparser
 from datetime import datetime
 import json
@@ -68,7 +67,7 @@ else:
 
 if os.path.exists(JSON_FILE):
     with open(JSON_FILE, encoding="utf8") as json_file:
-        json_dict = json.load(json_file)
+        json_dict = json.loads(json_file)
 
     PERIOD = json_dict["period"]
     lv_list = json_dict["lv_list"]
@@ -149,7 +148,7 @@ else:
             syncopts.append("--bwlimit=" + str(bwlimit))
 
 if not lv_list:
-    lv_list = ast.literal_eval(config.get(PERIOD, "backup_lvs"))
+    lv_list = json.loads(config.get(PERIOD, "backup_lvs"))
 
 stack_dict = {}