This fixes the bug - all apps built with gomobile build had the same
bundle id (org.golang.todo.main).
As part of this fix, rfc1034Label function is used to sanitize the app
name (in a similar way of 'rfc1034identifier' formatter). We use this
for Android app package name as well.
Change-Id: Iae1985614a55771bf1849fe66180c4ac736497d7
Reviewed-on: https://go-review.googlesource.com/13041
Reviewed-by: David Crawshaw <crawshaw@golang.org>