Revert "Generalize Installer::showStatusMessage()"

We probably want to put errors on top in the web installer
and warnings on top in the CLI installer due to differences
in scrolling.

This reverts commit 1c1e321af7977722073116fb6846f494502f6805.

Change-Id: I247030f0a3da6dff44884f4a282e52e92657fd91