remote-search: initialize the DBus proxy asynchronously

remote-search: initialize the DBus proxy asynchronously

Initializing this synchronously means that we will possibly wait for the
process to be auto-activated and answering to our call.
If the process is already running it also might not answer immediately
our request, as it might be doing sync I/O.
The right thing to do is to initialize the proxy asynchronously; there
are try/catch blocks in place for when the object is not available, or
not properly initialized.

https://bugzilla.gnome.org/show_bug.cgi?id=687491