[libc] Update buildbot worker version to 2.8.4.

Tested locally by connecting to LLVM master. (:
http://lab.llvm.org:8011/#/builders/78/builds/1

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D89069

libc/utils/buildbot/Dockerfile

@@ -6,7 +6,7 @@ RUN apt-get update
 RUN apt-get install -y build-essential clang subversion git vim \
   zip libstdc++6:i386 file binutils-dev binutils-gold cmake python-pip \
   ninja-build
-RUN python -m pip install buildbot-slave==0.8.12
+RUN python -m pip install buildbot-worker==2.8.4
 
 # Temporary dependencies for AOR tests.
 RUN apt-get install -y libmpfr-dev libmpc-dev

libc/utils/buildbot/run.sh

@@ -3,8 +3,8 @@
 # This serves as the entrypoint for docker to allow us to
 # run and start the buildbot while supplying the password
 # as an argument.
-buildslave create-slave --keepalive=200 "${WORKER_NAME}" \
+buildbot-worker create-worker --keepalive=200 "${WORKER_NAME}" \
   lab.llvm.org:9990 "${WORKER_NAME}" "$1"
 
-buildslave start "${WORKER_NAME}"
+buildbot-worker start "${WORKER_NAME}"
 tail -f ${WORKER_NAME}/twistd.log