sh: Test that executing various binary files is rejected

If executing a file fails with an [ENOEXEC] error, the shell executes the
file as a shell script, except that this execution may instead result in an
error message if the file is binary.

Per a recent Austin Group interpretation, we will need to change this to
allow a concatenation of a shell script and a binary payload. See
Austin Group bugs #1226 and #1250.

MFC after: 1 week

(cherry picked from commit 2a55bade0ed3e08a8c4f922df0ecf67d1ee32f53)