Filter out VENDOR_PYTHONPATH from PYTHONPATH in aosp.

Currently when switching between internal to aosp, PYTHONPATH will be
contaminated. This CL is to ensure PYTHONPATH will be as clean as
opening a new terminal and source/lunch.

Bug: 121106770

Test: internal:
$ source build/envsetup.sh; lunch; echo $PYTHONPATH| sed 's/:/\n/g'
will see VENDOR_PYTHONPATH in PYTHONPATH.

switch to aosp:
$ source build/envsetup.sh; lunch; echo $PYTHONPATH| sed 's/:/\n/g'
won't see VENDOR_PYTHONPATH in PYTHONPATH.

Change-Id: Id1916673000ee3fad55e9611d0c47cc80de86645
diff --git a/envsetup.sh b/envsetup.sh
index 9198ee5..0392e86 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -285,6 +285,9 @@
     fi
     # and in with the new
     export ANDROID_PYTHONPATH=$T/development/python-packages:
+    if [ -n $VENDOR_PYTHONPATH  ]; then
+        ANDROID_PYTHONPATH=$ANDROID_PYTHONPATH$VENDOR_PYTHONPATH
+    fi
     export PYTHONPATH=$ANDROID_PYTHONPATH$PYTHONPATH
 
     export ANDROID_JAVA_HOME=$(get_abs_build_var ANDROID_JAVA_HOME)
@@ -1552,6 +1555,7 @@
 #
 # This allows loading only approved vendorsetup.sh files
 function source_vendorsetup() {
+    unset VENDOR_PYTHONPATH
     allowed=
     for f in $(find -L device vendor product -maxdepth 4 -name 'allowed-vendorsetup_sh-files' 2>/dev/null | sort); do
         if [ -n "$allowed" ]; then