Update user variables to match common-packer

Update user variables to match common-packer

common-packer changes some of the variable names in order to
standardize with all the other clouds managed by LF. Let us update
the variables to match.

Change-Id: I7d3783fa728a51c86176a0325d0b69a1e0d9bea5
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>