[v1.9.x] CI fixes (#20648)

* Update openssl package in ubuntu_core.sh (used in ubuntu 16.04 images) to avoid bug triggered by let's encrypt expired ca cert.

* Reduce number of parallel docker builds we run at once to 2, since there are multiple jobs (on different branches) running at the same time.

* Use different mirror to download binutils to avoid expired let's encrypt CA cert.

Author: josephevans

ci/docker/install/ubuntu_binutils.sh

@@ -28,7 +28,7 @@ apt-get install -y \
     wget
 
 mkdir /opt/binutils_install && mkdir /opt/binutils && cd /opt/binutils
-wget -nv https://ftp.gnu.org/gnu/binutils/binutils-2.27.tar.gz
+wget -nv http://mirrors.kernel.org/gnu/binutils/binutils-2.27.tar.gz
 tar -xvf binutils-2.27.tar.gz && cd binutils-2.27
 ./configure --prefix=/opt/binutils_other --exec-prefix=/opt/binutils_install
 make -j$(nproc)

ci/docker/install/ubuntu_core.sh

@@ -51,6 +51,7 @@ apt-get install -y \
     libedit-dev \
     libxml2-dev \
     ninja-build \
+    openssl \
     software-properties-common \
     sudo \
     unzip \

ci/docker_cache.py

@@ -38,7 +38,7 @@
 
 DOCKER_CACHE_NUM_RETRIES = 3
 DOCKER_CACHE_TIMEOUT_MINS = 45
-PARALLEL_BUILDS = 5
+PARALLEL_BUILDS = 2
 DOCKER_CACHE_RETRY_SECONDS = 5
 DOCKER_BUILD_NUM_RETRIES = 2