Fix variable name in PostImportSetupScript

The section that alters the Primary HFS directory is using the old
variable name for the value we want to type

Replace "${SYSTEM_TEMP_DIR}" with ${TEST_VISTA_SETUP_PRIMARY_HFS_DIR}"

OSEHRA-Id: http://issues.osehra.org/browse/OAT-104
Change-Id: Ia56814291011945d3b610c43e78793b6a63c153c