let svn fetches print to stdout

Summary:
As we've done recently for hg and curl, let svn print its fetch progress
to stdout, so that the fancy display can show it.

Reviewers: sean

Differential Revision: https://phabricator.buildinspace.com/D96

peru/resources/plugins/svn/reup.py

@@ -10,7 +10,7 @@
 
 
 def remote_head_rev(url):
-    info = svn('info', url).split('\n')
+    info = svn('info', url, capture_output=True).split('\n')
     for item in info:
         if item.startswith('Revision: '):
             return item.split()[1]

peru/resources/plugins/svn/svn_plugin_shared.py

@@ -4,16 +4,18 @@
 import subprocess
 
 
-def svn(*args, svn_dir=None):
+def svn(*args, svn_dir=None, capture_output=False):
     # Avoid forgetting this arg.
     assert svn_dir is None or os.path.isdir(svn_dir)
 
     command = ['svn', '--non-interactive']
     command.extend(args)
 
+    stdout = subprocess.PIPE if capture_output else None
+    stderr = subprocess.STDOUT if capture_output else None
     process = subprocess.Popen(
-        command, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
-        stderr=subprocess.STDOUT, cwd=svn_dir, universal_newlines=True)
+        command, stdin=subprocess.PIPE, stdout=stdout, stderr=stderr,
+        cwd=svn_dir, universal_newlines=True)
     output, _ = process.communicate()
     if process.returncode != 0:
         raise RuntimeError(