clonebundle: update hook arguments (BC)

By calling applybundle() with 'clonebundles' and the url instead of
calling processbundle(), the hooks will get different arguments:
HG_SOURCE will be 'clonebundles' instead of 'bundle2' and HG_URL will
be the url instead of 'bundle2'. This is consistent with the bundle1
behavior and seems like a bug fix, but I'm marking it BC anyway.

mercurial/exchange.py

@@ -1997,7 +1997,7 b' def trypullbundlefromurl(ui, repo, url):'
             cg = readbundle(ui, fh, 'stream')
 
             if isinstance(cg, bundle2.unbundle20):
-                bundle2.processbundle(repo, cg, lambda: tr)
+                bundle2.applybundle(repo, cg, tr, 'clonebundles', url)
             elif isinstance(cg, streamclone.streamcloneapplier):
                 cg.apply(repo)
             else: