profiling: move 'fp' closing logic into its own function

profiling: move 'fp' closing logic into its own function

We are about to make the logic more robust and reuse it in more place, we start
by isolating what we have.

--- a/mercurial/profiling.py	Tue Jun 13 01:23:54 2017 +0530
+++ b/mercurial/profiling.py	Mon Jun 12 17:13:35 2017 +0200
@@ -218,4 +218,7 @@
                 # so we need to escape any % signs.
                 val = val.replace('%', '%%')
                 self._ui.log('profile', val)
-            self._fp.close()
+            self._closefp()
+
+    def _closefp(self):
+        self._fp.close()