Include clone_speedup_options in git fetch

This change is not only performance related, it should also fix the
missing blob object errors. Fetching with --filter=tree:0 should always
be more resilient to missing objects upstream

```
sh-5.1$ git fetch -f https://github.com/alisw/alibuild-recipe-tools
+refs/tags/*:refs/tags/* +refs/heads/*:refs/heads/*
remote: Enumerating objects: 8, done.
remote: Counting objects: 100% (8/8), done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 6 (delta 2), reused 6 (delta 2), pack-reused 0
Unpacking objects: 100% (6/6), 806 bytes | 806.00 KiB/s, done.
fatal: missing blob object '6f314120ba0359d1f73ad7d1d4a7f171fb36e8ac'
error: https://github.com/alisw/alibuild-recipe-tools did not send all necessary objects
```

Author: singiamtel

alibuild_helpers/git.py

@@ -8,8 +8,13 @@
 """How many seconds to let any git command execute before being terminated."""
 
 
+# Don't recalculate this every time we need it.
+_clone_speedup_cache = None
 def clone_speedup_options():
   """Return a list of options supported by the system git which speed up cloning."""
+  if _clone_speedup_cache is not None:
+    return _clone_speedup_cache
+
   for filter_option in ("--filter=tree:0", "--filter=blob:none"):
     _, out = getstatusoutput("LANG=C git clone " + filter_option)
     if "unknown option" not in out and "invalid filter-spec" not in out:
@@ -63,7 +68,7 @@ def checkoutCmd(self, ref):
     return ["checkout", "-f", ref]
 
   def fetchCmd(self, source, *refs):
-    return ["fetch", "-f", source, *refs]
+    return ["fetch", "-f"] + clone_speedup_options() + [source, *refs] 
 
   def setWriteUrlCmd(self, url):
     return ["remote", "set-url", "--push", "origin", url]