Can not set array value in dictionary from python

[frenchdog]

Description of Issue

Setting an array of string in the customLayerData field of a layer does not work in Python

Steps to Reproduce

Running following code

d = {'foo': ['x', 'y']}
stage.SetMetadata('customLayerData', d)

create an invalid data looking like this

(

    customLayerData = {

         foo = [x, y]

    }

)

System Information (OS, Hardware)

OSX and Linux

Package Versions

v19.05

[jilliene]

Filed as internal issue #USD-5200