cutils: fix memory leak in get_relocated_path()

cutils: fix memory leak in get_relocated_path()

get_relocated_path() allocates a GString object and returns the
character data (C string) to the caller without freeing the memory
allocated for that object as reported by valgrind:

  24 bytes in 1 blocks are definitely lost in loss record 2,805 of 6,532
     at 0x4839809: malloc (vg_replace_malloc.c:307)
     by 0x55AABB8: g_malloc (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x55C2481: g_slice_alloc (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x55C4827: g_string_sized_new (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x55C4CEA: g_string_new (in /usr/lib64/libglib-2.0.so.0.6600.8)
     by 0x906314: get_relocated_path (cutils.c:1036)
     by 0x6E1F77: qemu_read_default_config_file (vl.c:2122)
     by 0x6E1F77: qemu_init (vl.c:2687)
     by 0x3E3AF8: main (main.c:49)

Let's use g_string_free(gstring, false) to free only the GString object
and transfer the ownership of the character data to the caller.

Fixes: f4f5ed2cbd ("cutils: introduce get_relocated_path")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210412170255.231406-1-sgarzare@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>