test: update powertest expected help message output

tests/gen/ptest_2439b7d68089135b.stdout

@@ -58,8 +58,8 @@ LONG VIEW OPTIONS
   -U, --created              use the created timestamp field
   --changed                  use the changed timestamp field
   --time-style               how to format timestamps (default, iso, long-iso,
-                             full-iso, relative, or a custom style with '+' as
-                             prefix. Ex: '+%Y/%m/%d')
+                             full-iso, relative, or a custom style '+<FORMAT>'
+                             like '+%Y-%m-%d %H:%M')
   --total-size               show the size of a directory as the size of all
                              files and directories inside (unix only)
   --no-permissions           suppress the permissions field

tests/ptests/ptest_2439b7d68089135b.stdout

@@ -58,8 +58,8 @@ LONG VIEW OPTIONS
   -U, --created              use the created timestamp field
   --changed                  use the changed timestamp field
   --time-style               how to format timestamps (default, iso, long-iso,
-                             full-iso, relative, or a custom style with '+' as
-                             prefix. Ex: '+%Y/%m/%d')
+                             full-iso, relative, or a custom style '+<FORMAT>'
+                             like '+%Y-%m-%d %H:%M')
   --total-size               show the size of a directory as the size of all
                              files and directories inside (unix only)
   --no-permissions           suppress the permissions field