A system UI cannot be controlled by appman-controller without installed dbus

It is possible to run System UI without pre-installed dbus and it can't be managed through appman-controller.

Run example:

/path/to/installed/automotive/qt/bin/appman --verbose -c am-config.yaml

Console output:

...

[WARN | am.system] Disabling external D-Bus interfaces: could not start a dbus-daemon process (/usr/local/bin/dbus-daemon): execvp: No such file or directory [main.cpp:1025]

...

Possible solutions (can be combined):

• notify user somehow
  • provide them possibility to quick&easy dbus installation
• update prerequisites information into documentation
• add some environment checks at startup/run/build operations
  • add Qt Auto output console for such information