[buildbot] docker,worker: install qemu-utils

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch staging/ynezz/buildbot-2.10.0:
https://git.openwrt.org/79a6dd008eb7e75f2237161e5fffc66dc5e78c0b

commit 79a6dd008eb7e75f2237161e5fffc66dc5e78c0b
Author: Paul Spooren <mail at aparcar.org>
AuthorDate: Sun Jan 10 10:27:58 2021 -1000

    docker,worker: install qemu-utils
    
    To convert x86 images to VDI/VMDK the `qemu-img` tools is required,
    which is part of Debians `qemu-utils` package. The goal is to remove the
    ancient in-tree `qemu-img` version and replace it with a recent host
    installed package.
    
    Related: https://github.com/openwrt/openwrt/pull/3739/
    
    Signed-off-by: Paul Spooren <mail at aparcar.org>
    [rebased]
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 docker/buildslave/Dockerfile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docker/buildslave/Dockerfile b/docker/buildslave/Dockerfile
index 405183a..6b09b37 100644
--- a/docker/buildslave/Dockerfile
+++ b/docker/buildslave/Dockerfile
@@ -28,6 +28,7 @@ RUN \
 		pwgen \
 		python3 \
 		python3-pip \
+		qemu-utils \
 		unzip \
 		wget && \
 	apt-get clean && \