Quieten the svn (or svnlite) commands used to extract information from an
SVN checkout for placement into an EC2 AMI. We only run these if there
is a .svn directory; but in the event that SVN was used to check out a
tree which is then exported over NFS, we were unnecessarily noisy.
Reported by: Andrey Fesenko
MFC after: 3 days
X-MFC-With: r336420, r336433, r336593, r336621,
r336622, r336624, r337394, r337401