With the plan to call curtin multiple times where each invocation has a
specific purpose, we want the client to have a simple way to monitor the
status of the installation.
Instead of defining new application states for each stage, we will
report the more generic WAITING / RUNNING states in a loop until we get
to the final stages of the installation.
To start with, we are dropping POST_WAIT and POST_RUNNING in favor or
WAITING and RUNNING.
Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>