Fix push file size test

What does this MR do?

Application settings are cached for up to a minute. So when we change the receive_max_input_size setting, the setting might not be applied for minute. This caused the tests to intermittently fail.

Most of the time the setting is updated in under a minute, so instead of waiting a minute after changing the setting we retry the attempt to push if it fails (6 attempts with 10s between attempts).

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30233#note_188616863

Closes https://gitlab.com/gitlab-org/quality/nightly/issues/113

Does this MR meet the acceptance criteria?

Conformity

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