Allow using toolchain.update() without feed URL
Allow using toolchain.update() without feed URL

This will just use the previously saved feed

Change-Id: I37f0052bde7c1616f26ecb1a1b5090d98cf0d9b8

dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild