Revise method fetching metadata using lazy wheels

* Rename it to fit the fact that it no longer handle
  fetching _not_ using lazy wheels
* Use self as the first parameter
* Unnest the checks with additional logs showing reason
  when lazy wheel is not used

Author: McSinyx

src/pip/_internal/operations/prepare.py

@@ -9,7 +9,6 @@
 import os
 import shutil
 
-from pip._vendor.contextlib2 import suppress
 from pip._vendor.packaging.utils import canonicalize_name
 from pip._vendor.six import PY2
 
@@ -462,7 +461,7 @@ def _get_linked_req_hashes(self, req):
         # showing the user what the hash should be.
         return req.hashes(trust_internet=False) or MissingHashes()
 
-    def _fetch_metadata(preparer, link):
+    def _fetch_metadata_using_lazy_wheel(self, link):
         # type: (Link) -> Optional[Distribution]
         """Fetch metadata using lazy wheel, if possible."""
         if not self.use_lazy_wheel:
@@ -497,7 +496,8 @@ def prepare_linked_requirement(self, req, parallel_builds=False):
         assert req.link
         link = req.link
         self._log_preparing_link(req)
-        wheel_dist = self._fetch_metadata(link)
+        with indent_log():
+            wheel_dist = self._fetch_metadata_using_lazy_wheel(link)
         if wheel_dist is not None:
             req.needs_more_preparation = True
             return wheel_dist