error: Use error_report_err() where appropriate

Coccinelle semantic patch:

    @@
    expression E;
    @@
    -    error_report("%s", error_get_pretty(E));
    -    error_free(E);
    +    error_report_err(E);
    @@
    expression E, S;
    @@
    -    error_report("%s", error_get_pretty(E));
    +    error_report_err(E);
    (
         exit(S);
    |
         abort();
    )

Trivial manual touch-ups in block/sheepdog.c.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/qemu-io.c b/qemu-io.c
index 91a445a..d7a32e4 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -464,8 +464,7 @@
     }
 
     if (qemu_init_main_loop(&local_error)) {
-        error_report("%s", error_get_pretty(local_error));
-        error_free(local_error);
+        error_report_err(local_error);
         exit(1);
     }