Add a script to upload nightly packages to S3

The nightly package name includes the date, and so we use a glob to
locate the package file without hard coding a value. However, globbing
will not work with our Buildbot steps setup because we perform word
splitting ourselves and pass an array to Buildbot, which will directly
exec the array instead of passing it to the shell, meaning globbing
does not occur. Instead, add a script to the servo repo where we can
use globbing, and use `shopt -s failglob` to guard against bad globs.

etc/ci/upload_nightly.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
+shopt -s failglob
+
+
+usage() {
+    printf "usage: ${0} android|linux|mac|windows\n"
+}
+
+
+upload() {
+    s3cmd put "${2}" "s3://servo-developer-preview/nightly/${1}"
+}
+
+
+main() {
+    if [[ "$#" != 1 ]]; then
+        usage >&2
+        return 1
+    fi
+
+    local platform package
+    platform="${1}"
+
+    if [[ "${platform}" == "android" ]]; then
+        package=target/arm-linux-androideabi/release/*.apk
+    elif [[ "${platform}" == "linux" ]]; then
+        package=target/*.tar.gz
+    elif [[ "${platform}" == "mac" ]]; then
+        package=target/*.dmg
+    elif [[ "${platform}" == "windows" ]]; then
+        package=target/*.tar.gz
+    else
+        usage >&2
+        return 1
+    fi
+
+    # Lack of quotes on package allows glob expansion
+    # Note that this is not robust in the case of embedded spaces
+    # TODO(aneeshusa): make this glob robust using e.g. arrays or Python
+    upload "${platform}" ${package}
+}
+
+main "$@"