The || and && operators to chain commands rely on the LHS command
to be successful (or unsucessful) to decide upon launching the RHS
command.

Unfortunately, success/failure is not always when errorlevel is
0 (non zero).

Some exmaples:
- if a redirection fails (eg. appending to a non existing file),
  the command (builtin/external) is always unsuccessful (and the
  error level is untouched,
- external command (when redirection is ok) is succesful when
  program exit code is zero,
- ditto for a call to a label inside the batch file, with
  the 'exit /b' parameter,
- it's way more complicated for builtins. Eg 'type' is unsuccessful
  on a non existing file, while 'dir' (on the same unexisting file)
  succeeds.

So start adding some tests about success / failure of some commands.
Signed-off-by: Eric Pouech <epouech@codeweavers.com>