Use a pipe instead of a fifo during installation

bash's anonymous fifos are only available if devfs is mounted.
On a system without /dev mounted (which is perfectly reasonable for a locked-down security testing machine), installing beef fails with (after applying #923)

    install-beef: line 81: /dev/fd/62: No such file or directory

This commit fixes and lets the installation run through.
Merge pull request #924 from phihag/install-pipeline-instead-of-fifo

Use a pipe instead of a fifo during installation