This reverts commit 06a19921.

What I haven't realized when writing this ^^ commit is that the
virQEMUDriver structure already stores the root directory path.
And since the pointer is immutable it can be accessed right from
the structure and thus there is no need to duplicate it in the
driver config.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>