bundle2: lazily iterate over bundle parts in the test
We used to create a list to know the number of parts in the bundle. This prevents
any lazy reading as planned for real usage.
The list creation is dropped. Some test output changed as debug output is
now interleaved with command output.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state