scripts: support building command SKIP_RM_OUTDIR=1 for smarthome [1/1]

PD#SWPL-161245

Problem:
building command SKIP_RM_OUTDIR=1 will fail because last build remain
the staging dir

Solution:
remove staging dir in last build

Verify:
local

Change-Id: I057b5d33def309197b43627ff88976a86580ce4a
Signed-off-by: Dezhen Wang <dezhen.wang@amlogic.com>
4 files changed