Cleaned up the installer output behavior.

This change also makes sure the logger handlers are not alterated after an
installation. That also fixes the remaining environment alteration issue in
test_packaging.
diff --git a/Lib/packaging/pypi/simple.py b/Lib/packaging/pypi/simple.py
index ee7a113..983d477 100644
--- a/Lib/packaging/pypi/simple.py
+++ b/Lib/packaging/pypi/simple.py
@@ -118,9 +118,10 @@
     def __init__(self, index_url=DEFAULT_SIMPLE_INDEX_URL, prefer_final=False,
                  prefer_source=True, hosts=DEFAULT_HOSTS,
                  follow_externals=False, mirrors_url=None, mirrors=None,
-                 timeout=SOCKET_TIMEOUT, mirrors_max_tries=0):
+                 timeout=SOCKET_TIMEOUT, mirrors_max_tries=0, verbose=False):
         super(Crawler, self).__init__(prefer_final, prefer_source)
         self.follow_externals = follow_externals
+        self.verbose = verbose
 
         # mirroring attributes.
         parsed = urllib.parse.urlparse(index_url)
@@ -184,7 +185,7 @@
         if predicate.name.lower() in self._projects and not force_update:
             return self._projects.get(predicate.name.lower())
         prefer_final = self._get_prefer_final(prefer_final)
-        logger.info('reading info on PyPI about %s', predicate.name)
+        logger.debug('Reading info on PyPI about %s', predicate.name)
         self._process_index_page(predicate.name)
 
         if predicate.name.lower() not in self._projects:
@@ -321,8 +322,9 @@
                                 infos = get_infos_from_url(link, project_name,
                                             is_external=not self.index_url in url)
                             except CantParseArchiveName as e:
-                                logger.warning(
-                                    "version has not been parsed: %s", e)
+                                if self.verbose:
+                                    logger.warning(
+                                        "version has not been parsed: %s", e)
                             else:
                                 self._register_release(release_info=infos)
                         else: