eventd/plugins: Split args for plugin command

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
autotools: Use AM_CPPFLAGS

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
libeventd-plugin: Fix G_LOG_DOMAIN

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
eventdctl: Change exit status

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
eventdctl: Retrieve return code from eventd

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
eventdctl: Report plugin errors

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
eventd/plugins: Allow plugins to report control command errors

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>