How do I skip an Android system update and stop its notifications?

I get a message

Android 5.0.1 System Update Available

but no option to skip the update.

In frustration, I click "download". It's not better after the download. I still get

System update downloaded

with no option to avoid the update.

How do I signal that I am perfectly content with KitKat 4.4.4 for the time being? I use my phone for development and want to be certain my development tools are ready before upgrading. In the meantime I also want to stop the continuous harassment via notifications. Is this possible? I am using a Nexus 5 and the phone is not rooted (I prefer it to stay that way).