[application] application installation should not cause termination of all the running apps

Before the change installation of any application, having the main document,
caused xwalk process termination (and hence termination of all the running
applications).
This patch fixes it so that only the installation-related application is
terminated and the rest applications remain being active.
Merge pull request #1852 from pozdnyakov/Install_with_main_doc

[application] application installation causes termination of all the running apps