[buildbot] docker: install `mkisofs` to worker container

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch master:
https://git.openwrt.org/b5fe0a11ac3427fb42203cc33ea84160818b073e

commit b5fe0a11ac3427fb42203cc33ea84160818b073e
Author: Paul Spooren <mail at aparcar.org>
AuthorDate: Fri Sep 3 08:39:47 2021 -1000

    docker: install `mkisofs` to worker container
    
    x86 targets allow the creation of ISO images, however this is not
    possible because the `mkisofs` is missing. Install it.
    
    Signed-off-by: Paul Spooren <mail at aparcar.org>
---
 docker/buildworker/Dockerfile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docker/buildworker/Dockerfile b/docker/buildworker/Dockerfile
index fdbae1f..5219f92 100644
--- a/docker/buildworker/Dockerfile
+++ b/docker/buildworker/Dockerfile
@@ -19,6 +19,7 @@ RUN \
 		curl \
 		gawk \
 		gcc-multilib \
+		genisoimage \
 		git-core \
 		gosu \
 		libdw-dev \