CI: Use packaged version of Verilator

Reduce CI times by using a packaged version of Verilator. The packaging
is done by me on Open Build Service, which provides Verilator packages
for various distributions. The packages are versioned to help choose the
exact version in CI.

This is experimental for now, let's see if that's a suitable path
forward in the longer term.

azure-pipelines.yml

@@ -6,8 +6,7 @@
 # Documentation at https://aka.ms/yaml
 
 variables:
-  VERILATOR_VERSION: 4.028
-  VERILATOR_PATH: /opt/buildcache/verilator/$(VERILATOR_VERSION)
+  VERILATOR_VERSION: 4.032
   RISCV_TOOLCHAIN_TAR_VERSION: 20200323-1
   RISCV_COMPLIANCE_GIT_VERSION: 844c6660ef3f0d9b96957991109dfd80cc4938e2
   VERIBLE_VERSION: v0.0-266-g9e55307
@@ -46,6 +45,9 @@ jobs:
   # information is not read, pip installs the latest version, which then fails
   # to run.
   - bash: |
+      curl -L https://download.opensuse.org/repositories/home:phiwag:edatools/xUbuntu_16.04/Release.key | sudo apt-key add -
+      sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/phiwag:/edatools/xUbuntu_16.04/ /' > /etc/apt/sources.list.d/edatools.list"
+      sudo apt-get update
       sudo apt-get install -y \
           python3 \
           python3-pip \
@@ -61,6 +63,7 @@ jobs:
           curl \
           libelf-dev \
           clang-format \
+          verilator-$(VERILATOR_VERSION) \
         && sudo pip3 install -U setuptools pip six \
         && sudo pip3 install -U -r python-requirements.txt
     displayName: Install dependencies
@@ -75,25 +78,6 @@ jobs:
       echo "##vso[task.setvariable variable=PATH]/tools/verible/bin:$PATH"
     displayName: Install Verible
 
-  - bash: |
-      set -e
-      if [ ! -d $(VERILATOR_PATH) ]; then
-        echo "Building verilator (no cached build found)"
-        mkdir -p build/verilator
-        cd build/verilator
-        curl -Ls -o verilator.tgz https://www.veripool.org/ftp/verilator-$(VERILATOR_VERSION).tgz
-        tar -xf verilator.tgz
-        cd verilator-$(VERILATOR_VERSION)
-        ./configure --prefix=$(VERILATOR_PATH)
-        make -j$(nproc)
-        mkdir -p $VERILATOR_PATH
-        make install
-      else
-        echo "Re-using cached verilator build"
-      fi
-      echo "##vso[task.setvariable variable=PATH]$VERILATOR_PATH/bin:$PATH"
-    displayName: Build and install Verilator
-
   - bash: |
       export TOOLCHAIN_URL=https://github.com/lowRISC/lowrisc-toolchains/releases/download/${RISCV_TOOLCHAIN_TAR_VERSION}/lowrisc-toolchain-gcc-rv32imc-${RISCV_TOOLCHAIN_TAR_VERSION}.tar.xz
       mkdir -p build/toolchain