Test: Fall back action runner to Ubuntu 20.04

.github/workflows/ubuntu.yaml

@@ -40,22 +40,24 @@ jobs:
   #      run: cd build && make
   #    - name: C++ test
   #      run: build/bin/test_singa
- 
+
   build-cpptest-on-cpu:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - uses: actions/checkout@v1
       - name: get-oneDNN
         run: wget https://github.com/oneapi-src/oneDNN/releases/download/v1.1/dnnl_lnx_1.1.0_cpu_gomp.tgz -P /tmp/ && tar zxf /tmp/dnnl_lnx_1.1.0_cpu_gomp.tgz -C /tmp
+      - name: setup-sys-env
+        run: sudo apt-get install -y curl wget git cmake
       - name: install-build-dependencies
         run: sudo apt-get install -y libgoogle-glog-dev libprotobuf-dev protobuf-compiler libncurses-dev libopenblas-dev gfortran libblas-dev liblapack-dev libatlas-base-dev swig dh-autoreconf lcov
       - name: configure
         run: mkdir build && cd build && cmake -DUSE_PYTHON=NO -DENABLE_TEST=YES -DCODE_COVERAGE=YES -DUSE_DNNL=YES ..
         env:
-         DNNL_ROOT: /tmp/dnnl_lnx_1.1.0_cpu_gomp/
+          DNNL_ROOT: /tmp/dnnl_lnx_1.1.0_cpu_gomp/
       - name: build
-        run: cd build && make
+        run: cd build && make -j8
       - name: C++ test
         run: build/bin/test_singa
       - name: Upload coverage to Codecov