build_android_sandboxed.py to allow multiple --readonly_bind_mount

Add action='append' to the argument readonly_bind_mount so that we can
specify multiple readonly bind mount paths for the builds. Interface
build_android_sandboxed.build() is also changed:
- readonly_bind_mount: A string path
+ readonly_bind_mounts: A list of string paths

Bug: 186381711
Test: Built on AB
Change-Id: I587c6b6e68edee6163391d6e155213b3d993098a
1 file changed