scm: Open stdout in text mode for Git timestamp subprocesses

Mock would fail when using SCM with Git timestamps from attempting
to mix encoded text strings with raw bytes since these subprocesses
weren't using an encoding for their output.

Omit showing the patch along with the timestamp.  It will break the
encoding if the diff contains invalid UTF-8 sequences.

mock/py/mockbuild/scm.py

@@ -114,14 +114,18 @@ def adjust_git_timestamps(self):
         cwd_dir = util.pretty_getcwd()
         self.log.debug("Adjusting timestamps in %s", self.src_dir)
         os.chdir(self.src_dir)
-        proc = subprocess.Popen(['git', 'ls-files', '-z'], shell=False, stdout=subprocess.PIPE)
+        proc = subprocess.Popen(
+            ['git', 'ls-files', '-z'],
+            shell=False, stdout=subprocess.PIPE, universal_newlines=True,
+        )
         for f in proc.communicate()[0].split('\0')[:-1]:
             rev = subprocess.Popen(
-                ['git', 'rev-list', 'HEAD', f], shell=False, stdout=subprocess.PIPE
+                ['git', 'rev-list', 'HEAD', f],
+                shell=False, stdout=subprocess.PIPE, universal_newlines=True,
             ).stdout.readlines()[0].rstrip('\n')
             ts = subprocess.Popen(
-                ['git', 'show', '--pretty=format:%ai', '--abbrev-commit', rev, f],
-                shell=False, stdout=subprocess.PIPE
+                ['git', 'show', '--pretty=format:%ai', '--no-patch', rev, f],
+                shell=False, stdout=subprocess.PIPE, universal_newlines=True,
             ).stdout.readlines()[0].rstrip('\n')
             subprocess.Popen(['touch', '-d', ts, f], shell=False)
         os.chdir(cwd_dir)