Merge "Add a variable to specify standalone system server jars." am:...

Merge "Add a variable to specify standalone system server jars." am: 1ecb2f95 am: 4207daaf am: bfa878e9 am: 459584be

Original change: https://android-review.googlesource.com/c/platform/build/+/1874113

Change-Id: I431fc53f33c64893efdbf7574d87e82592626f75