tests: use correct a11y application name

https://bugzilla.gnome.org/show_bug.cgi?id=725219
tests: kill gnome-software after each test

https://bugzilla.gnome.org/show_bug.cgi?id=725219
tests: actions: press Esc instead of Close button (as dogtail can't do this now)

https://bugzilla.gnome.org/show_bug.cgi?id=725219
tests: open Software Sources dialog

https://bugzilla.gnome.org/show_bug.cgi?id=725219
tests: Details page

https://bugzilla.gnome.org/show_bug.cgi?id=725219
Call g_set_prgname to set correct name for a11y tests

By default pyatspi will use binary name for application, g_set_prgname will
update it to required value. Gnome-weather does the similar trick in
package.js

This commit also updates tests