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-nbd.c b/qemu-nbd.c
index 4d8df08..2ba2d4c 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -228,8 +228,7 @@
     int fd = inet_listen(address_and_port, NULL, 0, SOCK_STREAM, 0, &local_err);
 
     if (local_err != NULL) {
-        error_report("%s", error_get_pretty(local_err));
-        error_free(local_err);
+        error_report_err(local_err);
     }
     return fd;
 }
@@ -240,8 +239,7 @@
     int fd = unix_listen(path, NULL, 0, &local_err);
 
     if (local_err != NULL) {
-        error_report("%s", error_get_pretty(local_err));
-        error_free(local_err);
+        error_report_err(local_err);
     }
     return fd;
 }
@@ -252,8 +250,7 @@
     int fd = unix_connect(path, &local_err);
 
     if (local_err != NULL) {
-        error_report("%s", error_get_pretty(local_err));
-        error_free(local_err);
+        error_report_err(local_err);
     }
     return fd;
 }
@@ -681,8 +678,7 @@
     }
 
     if (qemu_init_main_loop(&local_err)) {
-        error_report("%s", error_get_pretty(local_err));
-        error_free(local_err);
+        error_report_err(local_err);
         exit(EXIT_FAILURE);
     }
     bdrv_init();