mononoke: fix flakiness of test-gettreepack.t

Summary:
The reason for flakiness was in unpredictable order of the tree items from
Mononoke. In the first gettreepack call we request two different revisions, and
Mononoke can return them in any order. hg handles it just fine (see updated
test with `hgmn up ...`), but hashes of the tree packs may change.

To remove flakiness let's not rely on the treepack files hash

Reviewed By: farnz

Differential Revision: D7237559

fbshipit-source-id: c04e9d45c41f1d288a90706d0ecc27ede36f8008

tests/integration/test-gettreepack.t

@@ -74,12 +74,24 @@ hg prefetch failed for treeonly repos. We can use it instead when it's fixed
 
 Make sure that new entries were downloaded
   $ [[ -a $TESTTMP/cachepath/repo/packs/manifests ]]
-  $ ls $TESTTMP/cachepath/repo/packs/manifests
-  14d5757b02d7849c29f5330a9784cde6ea705b10.dataidx
-  14d5757b02d7849c29f5330a9784cde6ea705b10.datapack
-  19f8819363e37aac879d4b9d262a6f159c2f499e.histidx
-  19f8819363e37aac879d4b9d262a6f159c2f499e.histpack
-  2b552b0b3dee8707b0d8e59440602314c30e7c48.histidx
-  2b552b0b3dee8707b0d8e59440602314c30e7c48.histpack
-  bd34d6c34ee406323fec52573c480997f38ae742.dataidx
-  bd34d6c34ee406323fec52573c480997f38ae742.datapack
+  $ ls $TESTTMP/cachepath/repo/packs/manifests | wc -l
+  8
+
+Update to the revisions. Make sure that gettreepack command is not sent because
+we've already downloaded all the trees
+  $ hgmn up 2 --debug | grep 'sending .* command'
+  sending hello command
+  sending between command
+  sending getfiles command
+  $ ls
+  A
+  B
+  C
+
+No wireproto commands should be sent at all, because everything has been already
+downloaded
+  $ hgmn up 1 --debug | grep 'sending .* command'
+  [1]
+  $ ls
+  A
+  B