The ornamental design for a container dolly, as shown and described.
FIG. 1 is a top right rear isometric view of the container dolly of the present invention;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a top left front isometric view thereof; and,
FIG. 9 is a perspective view thereof.
The portions of the container dolly illustrated in broken lines form no part of the claimed design. The container shown in broken lines in FIG. 9 is to show environment and forms no part of the claimed design.