Avoid trying to read from stdin where this is not useful

[karenetheridge]

The --help, --version, --self-upgrade commands do not take additional
arguments, so it makes no sense to read from stdin for them. Otherwise,
we will block forever trying to read from stdin when doing
cpanm --version inside a remote script (where -t STDIN is false).

To test, yes | cpanm --version no longer hangs.

[zakame]

On a related note, is the !-t STDIN check useful here? I frequently run Emacs eshell (where TERM=dumb and pipes to STDIN opens to a tty) so something like echo Moose | cpanm won't work on such shells.

Removing !-t STDIN would make it work; let me know if its something so I could make a new issue/PR if needed.

Edit: mixed up my checks here...

[miyagawa]

@zakame removing that check would make cpanm block on input if you run from a shell.

In a hindsight this "read from STDIN" should be on its own option rather than DWIMing it.