test: use bundle2 in test-http-proxy
The proxy test does not care about what protocol is used, but the new
protocol implies different traffic (and therefore different log
output). We switch it to bundle2 early to minimise the noise of using
bundle2 for exchange by default.
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present