travis: use bionic as default for Linux (#16521)

Modifications:

- [x] Travis now uses `bionic` as a default (`xenial` used for Python 3.5, `trusty` for Python 2.6)
- [x] Shell unit tests have been factored into their own run
- [x] `kcov` is built only for tests that upload coverage results

Overall with this we shave 3-4 mins. on each run and add an additional run of about 3 min. For some reason `kcov` 38 fails forwarding output when used with Python unit tests, so I used v34 for that and v38 (latest) for shell testing. Previously we were using v25.

.travis.yml

@@ -12,7 +12,7 @@ branches:
 # Build matrix
 #=============================================================================
 
-dist: xenial
+dist: bionic
 
 jobs:
   fast_finish: true
@@ -32,27 +32,22 @@ jobs:
           # Everything but patchelf, that is not available for trusty
           packages:
             - ccache
-            - cmake
             - gfortran
             - graphviz
             - gnupg2
             - kcov
             - mercurial
             - ninja-build
-            - perl
-            - perl-base
             - realpath
-            - r-base
-            - r-base-core
-            - r-base-dev
             - zsh
       env: [ TEST_SUITE=unit, COVERAGE=true ]
     - python: '2.7'
       os: linux
       language: python
-      env: [ TEST_SUITE=unit, COVERAGE=true ]
+      env: [ TEST_SUITE=unit, COVERAGE=true, KCOV_VERSION=34 ]
     - python: '3.5'
       os: linux
+      dist: xenial
       language: python
       env: TEST_SUITE=unit
     - python: '3.6'
@@ -66,7 +61,11 @@ jobs:
     - python: '3.8'
       os: linux
       language: python
-      env: [ TEST_SUITE=unit, COVERAGE=true ]
+      env: [ TEST_SUITE=unit, COVERAGE=true, KCOV_VERSION=34 ]
+    - python: '3.8'
+      os: linux
+      language: python
+      env: [ TEST_SUITE=shell, COVERAGE=true, KCOV_VERSION=38 ]
     - python: '3.8'
       os: linux
       language: python
@@ -87,20 +86,13 @@ addons:
   apt:
     packages:
       - ccache
-      - cmake
+      - coreutils
       - gfortran
       - graphviz
       - gnupg2
-      - kcov
       - mercurial
       - ninja-build
       - patchelf
-      - perl
-      - perl-base
-      - realpath
-      - r-base
-      - r-base-core
-      - r-base-dev
       - zsh
     update: true
 
@@ -114,6 +106,16 @@ cache:
 
 before_install:
   - ccache -M 2G && ccache -z
+  # Install kcov manually, since it's not packaged for bionic beaver
+  - if [[ "$KCOV_VERSION" ]]; then
+        sudo apt-get -y install cmake binutils-dev libcurl4-openssl-dev zlib1g-dev libdw-dev libiberty-dev;
+        KCOV_ROOT=$(mktemp -d);
+        wget --output-document=${KCOV_ROOT}/${KCOV_VERSION}.tar.gz https://github.com/SimonKagstrom/kcov/archive/v${KCOV_VERSION}.tar.gz;
+        tar -C ${KCOV_ROOT} -xzvf ${KCOV_ROOT}/${KCOV_VERSION}.tar.gz;
+        mkdir -p ${KCOV_ROOT}/build;
+        cd ${KCOV_ROOT}/build && cmake -Wno-dev ${KCOV_ROOT}/kcov-${KCOV_VERSION} && cd - ;
+        make -C ${KCOV_ROOT}/build && sudo  make -C ${KCOV_ROOT}/build install;
+    fi
 
 # Install various dependencies
 install:
@@ -151,6 +153,10 @@ after_success:
                         --flags "${TEST_SUITE}${TRAVIS_OS_NAME}";
             fi
             ;;
+        shell)
+            codecov --env PYTHON_VERSION
+            --required
+            --flags "${TEST_SUITE}${TRAVIS_OS_NAME}";
     esac
 
 #=============================================================================