new_variant: support volteer and volteer2

The volteer reference board is based on ES2 silicon, while volteer2
is based on QS silicon. For the fitimage, we need to differentiate
between the two, while all the other steps for creating a new
variant are identical.
* Add support to call a different script to add the new fitimage
* Add a new reference board support file for volteer2
* Update to support volteer2

TEST=Test both the "volteer" and "volteer2" reference boards:
`testdata/ volteer && echo PASS`
`testdata/ volteer2 && echo PASS`

Cq-Depend: chrome-internal:3460226
Change-Id: I720b7689cbb88729717796232b0664ba2293c4bb
Tested-by: Paul Fagerburg <>
Reviewed-by: YH Lin <>
Commit-Queue: Nick Vaccaro <>
5 files changed