FS.readPipe() shouldn't log IOException as an error

This unintentionally was changed from severity debug to error which is
causing unexpected log entries.

Bug: 463349
Change-Id: I4b6d42a1420652ab6824e237bd231ba86896acbf
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java

@@ -481,7 +481,7 @@ public abstract class FS {
 				}
 			}
 		} catch (IOException e) {
-			LOG.error("Caught exception in FS.readPipe()", e); //$NON-NLS-1$
+			LOG.debug("Caught exception in FS.readPipe()", e); //$NON-NLS-1$
 		}
 		if (debug) {
 			LOG.debug("readpipe returns null"); //$NON-NLS-1$