[Docker] more base images (#10560)

* Revert "work around an issue with docker/dockerhub (#10547)"

This reverts commit 0ef139ac4d.

* Add more docker base image configurations.

 - Renamed configs

   - "centos" -> "centos-7"
   - "fedora" -> "fedora-24"
   - "opensuse" -> "opensuse-tumbleweed"
   - "scilinux" -> "scilinux-7"
   - "ubuntu" -> "ubuntu-1804"

 - Added configs

   - "centos-6"
   - "fedora-29"
   - "opensuse-leap"
   - "scilinux-6"
   - "ubuntu-1604"

With these changes, our docker hub image
collection will consist of the following:

 - "spack/archlinux"
   - "latest"
 - "spack/centos"
   - "latest", "centos7", "7"
   - "centos6", "6"
 - "spack/fedora"
   - "latest", "29"
   - "24"
 - "spack/opensuse"
   - "latest", "tumbleweed"
   - "leap"
 - "spack/scilinux"
   - "latest", "7"
   - "6"
 - "spack/ubuntu"
   - "latest", "bionic", "18.04"
   - "xenial", "16.04"

share/spack/qa/run-docker-tests

@@ -21,23 +21,9 @@ ensure_docker_login() {
         return $__login_success
     fi
 
-    if [ "$CI" '=' 'true' -a "$TRAVIS" '=' 'true' ] ; then
-        # NOTE: work around an issue with docker/docker hub
-        # https://github.com/docker/hub-feedback/issues/1222
-        # https://github.com/docker/cli/issues/1180
-        rm -f $HOME/.docker/config.json
-    fi
-
     echo "$DOCKER_PASSWORD" | \
         docker login -u "$DOCKER_USERNAME" --password-stdin
 
-    if [ "$CI" '=' 'true' -a \
-         "$TRAVIS" '=' 'true' -a \
-         '!' -f "$HOME/.docker/config.json" ]
-    then
-        echo "Warning: config file $HOME/.docker/config.json not created" >&2
-    fi
-
     if [ $? '=' '0' ] ; then
           __login_success=0
     fi