test: explicitly disable sparse-revlog in test-http-bad-server.t

The `test-http-bad-server.t` test is very fragile with hard-coded number all
around. Adding any new capability have massive consequences on it that are
long and tiresome to handle. Since the test check more generic protocol level
behavior, it does not need to follow all new capabilities. Disabling the
capabilities is a much simpler way to avoid the issue.

We make sure `sparse-revlog` will not impact this test once turned on by
default.

Differential Revision: https://phab.mercurial-scm.org/D5313

tests/test-http-bad-server.t

@@ -11,6 +11,8 b' version so behavior is deterministic.'
   $ cat >> $HGRCPATH << EOF
   > [extensions]
   > fakeversion = `pwd`/fakeversion.py
+  > [format]
+  > sparse-revlog = no
   > [devel]
   > legacy.exchange = phases
   > EOF