acloud setup: User must explicitly pass in --host to do host setup.

Installing packages can be a sensitive affair so let's only do it if the
user really wants it.

Bug: 124268982
Test: acloud setup
acloud setup --host
acloud setup --gcp-init

Change-Id: I69b565f0b26d7690a8eed748351480b2bf0536fa
2 files changed