openssh/util-linux/python*: Ensure ptest output is unbuffered

We need to run sed with the -u option to ensure the output is unbuffered else
ptest-runner may timeout thinkig things were idle. Busybox doesn't have the -u
option so we need to RDEPEND on sed (which is a good thing to do if we use it
anyway).

Alex Kanavin should get credit for discovering the problem.

(From OE-Core rev: d3ffbebf43c23faa43af81c9ecf6fcaef36d675b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/util-linux/util-linux/run-ptest

@@ -16,7 +16,7 @@ res=0
 count=0
 for ts in $comps; 
 do 
-   $ts | sed '{        
+   $ts | sed -u '{        
       s/^\(.*\):\(.*\) \.\.\. OK$/PASS: \1:\2/                              
       s/^\(.*\):\(.*\) \.\.\. FAILED \(.*\)$/FAIL: \1:\2 \3/                
       s/^\(.*\):\(.*\) \.\.\. SKIPPED \(.*\)$/SKIP: \1:\2 \3/