msg: improve failure messages
msg: improve failure messages

Avoid saying "this system is not reliable" and provide
better instructions to the user.

Change-Id: I154aafcdef90c9ac1ddde2a66a986a8ed6635eb7
Bug-Url: https://bugzilla.redhat.com/1537588
Signed-off-by: Simone Tiraboschi <cb03129c66ba4da7ba7044049d0f43907bf857bb@redhat.com>

oVirt/ovirt-hosted-engine-setup,oVirt/ovirt-hosted-engine-setup