Finish and re-enable listing mode acceptance tests

test/data/config_cfgrep/list_keys.oracle.stdout

 key1
+key1
+key2
+key2
+key1
+key1
+key2
 key2

test/data/config_cfgrep/list_paths

 # desc: list paths
-# cmd: cfgrep -L paths
+# cmd: cfgrep -l -
 
 [section1]
 free form in s1

test/data/config_cfgrep/list_paths.oracle.stdout

 section1.key1
+section1.key1
+section1.key2
 section1.key2
 section2.key1
+section2.key1
+section2.key2
 section2.key2

test/data/config_cfgrep/list_sections

 # desc: list sections
-# cmd: cfgrep -L sections
+# cmd: cfgrep -L sections -
 
 [section1]
 free form in s1

test/scripts/config_cfgrep

     echo "tricks_with_strange_naming"
     echo "strict_and_space"
     echo "strict_and_tab"
-#   echo "list_keys"        # not implemented
-#   echo "list_paths"       # not implemented
-#   echo "list_sections"    # not implemented
+    echo "list_keys"
+    echo "list_paths"
+    echo "list_sections"
 }
 
 tf_do_subtests