update.py: support one-module-per-line configuration

Fixes bug #1122701

Allow:

  module=foo
  module=bar

rather than

  modules=foo,bar

to make reviewing changes easier.

Change-Id: Ic0a7fb28fd34f530c93806a5fb79ed3dc3bc494e
Merge "update.py: support one-module-per-line configuration"