unable to launch binary with arbitrary desktop file

[Gerry Boland]

Try the following:

1. Take a valid desktop file and copy it to a local place:
        cp /usr/share/applications/dialer-app.desktop /home/phablet/temp.desktop
2. Now use desktop_file_hint to launch an app
        dialer-app --desktop_file_hint=/home/phablet/temp.desktop

dialer-app will fail to launch, because unity8 rejects the connection:

qtmir.mir: SessionAuthorizer::connection_is_allowed - this= SessionAuthorizer(0xb1bf8514) pid= 6876
qtmir.applications: ApplicationManager::authorizeSession - pid= 6876
qtmir.applications: Process supplied desktop_file_hint, loading: "/home/phablet/temp.desktop"
qtmir.applications: Unable to find file: "/home/phablet/temp" so will search standard paths for one named "temp" .desktop
qtmir.applications: ApplicationController::desktopFilePathForAppId - appId= "temp"
qtmir.applications: Loading desktop file "" for appId "temp"
qtmir.applications: Desktop file for appId: "temp" at: "" does not exist
ApplicationManager REJECTED connection from app with pid 6876 as the file specified by the desktop_file_hint argument could not be opened