Switch to bufio Reader for exec streams

[haircommander]

There were many situations that made exec act funky with input. pipes didn't work as expected, as well as sending input before the shell opened.
Thinking about it, it seemed as though the issues were because of how os.Stdin buffers (it doesn't). Dropping this input had some weird consequences.
Instead, read from os.Stdin as bufio.Reader, allowing the input to buffer before passing it to the container.

Note: I think there are some missed edge cases that need hammering out, so I would say this is WIP until I know everything works as expected

fixes: #4397
fixes: #4326
fixes the open part of: #3302

Signed-off-by: Peter Hunt pehunt@redhat.com

[mheon]

Neat. Does this solve our pipe issues?

[haircommander]

"solve" as in the unix pipe issue disappears. It still doesn't really work as expected, or work like run does (echo hi | podman exec -til echo returns nothing) but the error disappears :D I think this is a good step to making pipes actually work

[mheon]

I think the way run does it might also be broken, though, so this could well be more correct than run.

[rhatdan]

@haircommander Seems to pass the tests.
LGTM
@vrothberg @giuseppe @baude PTAL

[vrothberg]

LGTM, can we remove the WIP?

[haircommander]

Sure, i think there's still work to be done but we're on the right track

[rhatdan]

/lgtm
/approve
Nice work @haircommander

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