Fix build issue when `/usr/bin/python` path is not available (#9547)

This fix tries to fix the build error where `PYTHON_BIN_PATH` is not
used in `tf_version_info_genrule()` (which will cause build error
if `python` is not available in the `PATH`).

This could be an issue even if `python` is available yet a different
python location is used in `./configure`.

This fix fixes the issue by passing `$(PYTHON_BIN_PATH)` explicitly
so that same python version could be used:
```udiff
-      "$(location //tensorflow/tools/git:gen_git_source.py) --generate $(SRCS) \"$@\"",
+      "$(PYTHON_BIN_PATH) $(location //tensorflow/tools/git:gen_git_source.py) --generate $(SRCS) \"$@\"",
```

See issue description:

In one of the build machines (Ubuntu 16.04) only python3 is available
(/usr/bin/python3) without python 2:
```
ubuntu@ubuntu:~/tensorflow$ python --version
python: command not found
ubuntu@ubuntu:~/tensorflow$ python3 --version
Python 3.5.2+
ubuntu@ubuntu:~/tensorflow$ which python3
/usr/bin/python3
```

After configure with `/usr/bin/python3`:
```
Please specify the location of python. [Default is /usr/bin/python3]:
...
```

The following is the error:
```
ubuntu@ubuntu:~/tensorflow$ bazel build --config=opt //tensorflow/tools/pip_package:build_pip_package
WARNING: /home/ubuntu/tensorflow/tensorflow/contrib/learn/BUILD:15:1: in py_library rule //tensorflow/contrib/learn:learn: target '//tensorflow/contrib/learn:learn' depends on deprecated target '//tensorflow/contrib/session_bundle:exporter': Use SavedModel Builder instead.
WARNING: /home/ubuntu/tensorflow/tensorflow/contrib/learn/BUILD:15:1: in py_library rule //tensorflow/contrib/learn:learn: target '//tensorflow/contrib/learn:learn' depends on deprecated target '//tensorflow/contrib/session_bundle:gc': Use SavedModel instead.
INFO: Found 1 target...
ERROR: /home/ubuntu/tensorflow/tensorflow/core/BUILD:1363:1: Executing genrule //tensorflow/core:version_info_gen failed: bash failed: error executing command /bin/bash -c ... (remaining 1 argument(s) skipped): com.google.devtools.build.lib.shell.BadExitStatusException: Process exited with status 127.
/usr/bin/env: 'python': No such file or directory
Target //tensorflow/tools/pip_package:build_pip_package failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 3.548s, Critical Path: 0.20s
```

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tensorflow/tensorflow.bzl b/tensorflow/tensorflow.bzl
index ddffabd8cb..7baddf301c 100644
--- a/tensorflow/tensorflow.bzl
+++ b/tensorflow/tensorflow.bzl
@@ -1185,7 +1185,7 @@ def tf_version_info_genrule():
       ],
       outs=["util/version_info.cc"],
       cmd=
-      "$(location //tensorflow/tools/git:gen_git_source.py) --generate $(SRCS) \"$@\"",
+      "$(PYTHON_BIN_PATH) $(location //tensorflow/tools/git:gen_git_source.py) --generate $(SRCS) \"$@\"",
       local=1,
       tools=[clean_dep("//tensorflow/tools/git:gen_git_source.py")],)