message: Update Ubuntu 14.04 variants to 16.04 and 16.04 variants to 18.04
diff: @@ -491,8 +491,8 @@ axes:
  - id: os
  display_name: "OS"
  values:
  - - id: "ubuntu-1404"
  - display_name: "Ubuntu 14.04 Debug"
  + - id: "ubuntu-1604"
  + display_name: "Ubuntu 16.04 Debug"
  variables:
  cdriver_configure_flags: *linux_cdriver_configure_flags
  extra_path: *linux_extra_path
  @@ -500,7 +500,7 @@ axes:
  build_type: "Debug"
  tar_options: *linux_tar_options
  run_on:
  - - ubuntu1404-test
  + - ubuntu1604-build
  - id: "windows-2k8"
  display_name: "Windows (VS 2015) Debug"
  variables:
  @@ -551,8 +551,8 @@ buildvariants:
  #######################################
  # Linux Buildvariants #
  #######################################
  - - name: ubuntu1404-release
  - display_name: "Ubuntu 14.04 Release"
  + - name: ubuntu1604-release
  + display_name: "Ubuntu 16.04 Release"
  expansions:
  build_type: "Release"
  tar_options: *linux_tar_options
  @@ -561,7 +561,7 @@ buildvariants:
  cmake_flags: *linux_cmake_flags
  mongodb_version: *version_latest
  run_on:
  - - ubuntu1404-test
  + - ubuntu1604-build
  tasks:
  - name: lint
  - name: compile_and_test_with_shared_libs
  @@ -569,21 +569,6 @@ buildvariants:
  - name: compile_and_test_with_shared_libs_replica_set
  - name: uninstall_check
  - - name: ubuntu1404-debug
  - display_name: "Ubuntu 14.04 Debug Static"
  - expansions:
  - build_type: "Debug"
  - tar_options: *linux_tar_options
  - cdriver_configure_flags: *linux_cdriver_configure_flags
  - extra_path: *linux_extra_path
  - cmake_flags: *linux_cmake_flags
  - mongodb_version: *version_latest
  - run_on:
  - - ubuntu1404-test
  - tasks:
  - # The debug shared lib is tested in the "integration tests" matrix
  - - name: compile_and_test_with_static_libs
  -
  - name: ubuntu1604-debug-std-experimental
  display_name: "Ubuntu 16.04 Debug (std::experimental)"
  expansions:
  @@ -691,8 +676,8 @@ buildvariants:
  - name: compile_and_test_with_shared_libs
  - name: compile_and_test_with_static_libs
  - - name: arm-ubuntu1604
  - display_name: "arm64 Ubuntu 16.04"
  + - name: arm-ubuntu1804
  + display_name: "arm64 Ubuntu 18.04"
  batchtime: 1440 # 1 day
  expansions:
  build_type: "Release"
  @@ -701,7 +686,7 @@ buildvariants:
  cmake_flags: *linux_cmake_flags
  mongodb_version: *version_latest
  run_on:
  - - ubuntu1604-arm64-small
  + - ubuntu1804-arm64-build
  tasks:
  - name: compile_and_test_with_shared_libs
  - name: compile_and_test_with_static_libs
  