Similarly to what virsh virt-login-shell do, call virAdmInitialize prior to
initializing an event loop and initializing the error handler. Commit 97973ebb
described and fixed an identical issue for libvirt_lxc.
Since virAdmInitialize becomes a public API after applying this patch,
the symbol is also added to public syms and the doc string of the method is
slightly enhanced analogically to virInitialize.
Signed-off-by: NErik Skultety <eskultet@redhat.com>