Disable sandboxed mode in bazel and use --spawn_strategy standalone

Encountered quite some issues with
```
Use --sandbox_debug to see verbose messages from the sandbox
/usr/bin/ld.gold: error: cannot find libavformat.so.57
/usr/bin/ld.gold: error: cannot find libavcodec.so.57
/usr/bin/ld.gold: error: cannot find libavutil.so.55
/usr/bin/ld.gold: error: cannot find libswscale.so.4
collect2: error: ld returned 1 exit status
Target //tensorflow_io/video:video_py_test failed to build
```

Believe it is related to (or similiar):
https://stackoverflow.com/questions/52386530/linker-fails-in-sandbox-when-running-through-bazel-but-works-when-sandboxed-comm?rq=1

Signed-off-by: Yong Tang <[email protected]>

Author: yongtang

.travis.yml

@@ -21,37 +21,37 @@ matrix:
       before_install:
         - bash -x ${TRAVIS_BUILD_DIR}/.travis/python.configure.sh
       script:
-        - bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
+        - bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
     - name: "Ubuntu 14.04 Python 3.4"
       language: python
       python:
         - 3.4
       before_install:
         - bash -x ${TRAVIS_BUILD_DIR}/.travis/python.configure.sh
       script:
-        - bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
+        - bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
     - name: "Ubuntu 14.04 Python 3.5"
       language: python
       python:
         - 3.5
       before_install:
         - bash -x ${TRAVIS_BUILD_DIR}/.travis/python.configure.sh
       script:
-        - bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
+        - bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
     - name: "Ubuntu 14.04 Python 3.6"
       language: python
       python:
         - 3.6
       before_install:
         - bash -x ${TRAVIS_BUILD_DIR}/.travis/python.configure.sh
       script:
-        - bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
+        - bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test -//tensorflow_io/video:video_py_test
     - name: "Ubuntu 18.04 Python 2.7"
       script:
-        - docker run -i -t -e PYTHON_VERSION= -e BAZEL_VERSION=0.20.0 -e BAZEL_OS=linux --rm -v $PWD:/workspace -w /workspace --net=host ubuntu:18.04 bash -x -c ".travis/python.ubuntu.18.04.sh && apt-get -y -qq install libavformat57 libavcodec57 libavutil55 libswscale4 && bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test"
+        - docker run -i -t -e PYTHON_VERSION= -e BAZEL_VERSION=0.20.0 -e BAZEL_OS=linux --rm -v $PWD:/workspace -w /workspace --net=host ubuntu:18.04 bash -x -c ".travis/python.ubuntu.18.04.sh && apt-get -y -qq install libavformat57 libavcodec57 libavutil55 libswscale4 && bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test"
     - name: "Ubuntu 18.04 Python 3.6"
       script:
-        - docker run -i -t -e PYTHON_VERSION=3 -e BAZEL_VERSION=0.20.0 -e BAZEL_OS=linux --rm -v $PWD:/workspace -w /workspace --net=host ubuntu:18.04 bash -x -c ".travis/python.ubuntu.18.04.sh && apt-get -y -qq install libavformat57 libavcodec57 libavutil55 libswscale4 && bazel test -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test"
+        - docker run -i -t -e PYTHON_VERSION=3 -e BAZEL_VERSION=0.20.0 -e BAZEL_OS=linux --rm -v $PWD:/workspace -w /workspace --net=host ubuntu:18.04 bash -x -c ".travis/python.ubuntu.18.04.sh && apt-get -y -qq install libavformat57 libavcodec57 libavutil55 libswscale4 && bazel test --spawn_strategy standalone -s --verbose_failures -- //tensorflow_io/... -//tensorflow_io/ignite:ignite_py_test"
     - name: "Ubuntu 14.04 R 3.2"
       language: r
       r: