test: use bundle2 for exchange in test-largefile
Using bundle2 for exchange unlock the usage of changegroup version 2. This
version of the changegroup held more information (delta base) that result in a
small increase in content size.
It also lead to reordering of output because the exchange scheduling is a bit
different.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a