Fix sdk-addon build on build servers

they don't source envsetup.sh

Bug: 65286453
Test: m -j OUT_DIR=/tmp/abs PRODUCT-sdk_gphone_x86-sdk_addon /tmp/abs/host/linux-x86/sdk_addon/google_phone_x86-eng.$(whoami)-linux-x86.zip

Change-Id: Id396203b500e70cfa2b1e1eb5241d88fae88fc36
Merged-In: Id396203b500e70cfa2b1e1eb5241d88fae88fc36
(cherry picked from commit 25210ce7)