arm64_download script waits for VM to boot before finishing.

It may take an unknown amount of time to boot.

Also, add `set -e` to the script to simplify error handling.

BUG=skia:2425
NOTRY=true
R=epoger@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/239243005

git-svn-id: http://skia.googlecode.com/svn/trunk@14209 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed