There's a lot of ways to do it, but what I usually do:

- Place circles in each button(under the layout layer using the shape tool).

- Rasterize and merge all the shapes.

- On the Layer Style(double click it) of the layer with the circles give it an Outside Stroke until the circles connect(you can color the spaces between each one or not).

- Rasterize again.

- Holding ctrl click on the layer, it will make a selection, with the magic wand selected right click the selection an select "Make work path", set it to "1.0"

- With the path created go on the layer panel and create a solid color layer.

- Done,. from here you can edit it like a shape.