fix(py): set cwd when get commit sha in setup.py (#14299)

`cwd` was not set before when get commit SHA. The default `cwd` is the current build directory. However, the build directory might not be the subdirectory of source. The `git` command will fail when that happened.

test=develop

Author: reyoung

python/setup.py.in

@@ -14,7 +14,8 @@ RC      = 0
 def git_commit():
     try:
         cmd = ['git', 'rev-parse', 'HEAD']
-        git_commit = subprocess.Popen(cmd, stdout = subprocess.PIPE).communicate()[0].strip()
+        git_commit = subprocess.Popen(cmd, stdout = subprocess.PIPE,
+            cwd="@PADDLE_SOURCE_DIR@").communicate()[0].strip()
     except:
         git_commit = 'Unknown'
     git_commit = git_commit.decode()
@@ -44,7 +45,7 @@ def get_patch():
 def is_taged():
     try:
         cmd = ['git', 'describe', '--exact-match', '--tags', 'HEAD', '2>/dev/null']
-        git_tag = subprocess.Popen(cmd, stdout = subprocess.PIPE).communicate()[0].strip()
+        git_tag = subprocess.Popen(cmd, stdout = subprocess.PIPE, cwd="@PADDLE_SOURCE_DIR@").communicate()[0].strip()
         git_tag = git_tag.decode()
     except:
         return False
@@ -55,8 +56,7 @@ def is_taged():
         return False
 
 def write_version_py(filename='paddle/version.py'):
-    cnt = '''
-# THIS FILE IS GENERATED FROM PADDLEPADDLE SETUP.PY
+    cnt = '''# THIS FILE IS GENERATED FROM PADDLEPADDLE SETUP.PY
 #
 full_version    = '%(major)d.%(minor)d.%(patch)s'
 major           = '%(major)d'