py3: replace file() with open() in test-clone.t

While I was here, I made sure we write things correctly in bytes mode.

Differential Revision: https://phab.mercurial-scm.org/D2110

tests/test-clone.t

@@ -10,7 +10,7 b' Prepare repo a:'
 
 Create a non-inlined filelog:
 
-  $ $PYTHON -c 'file("data1", "wb").write("".join("%s\n" % x for x in range(10000)))'
+  $ $PYTHON -c 'open("data1", "wb").write(b"".join(b"%d\n" % x for x in range(10000)))'
   $ for j in 0 1 2 3 4 5 6 7 8 9; do
   >   cat data1 >> b
   >   hg commit -m test