[Process] Redirect output without a shell

Currently processes that output large amounts of data will block. If
the output is not important then this becomes an issue. It can be worked
around by redirecting the output to > /dev/null but this requires an
instance of /bin/sh to do the work.

This patch adds the ability to set the processPipes, and a new
processPipe that redirects to /dev/null.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9007
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/3303