Split test kernel modules to a separate script.

Notice that Python sucks and does SIGPIPE annoyances, for now work around
by grepping the output file...

Fix the exit status read check with 'b', it broke down occasionally with:

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 1832: invalid start byte

README.adoc

@@ -10184,7 +10184,7 @@ Testing that should be done for every functional patch.
 
 ===== Guest testing
 
-Build for all stable archs and run basic fast tests:
+Run all tests:
 
 ....
 ./build-all
@@ -10199,6 +10199,15 @@ Sources:
 * link:build-all[]
 * link:test[]
 
+Test just the kernel modules:
+
+....
+./test-kernel-modules
+echo $?
+....
+
+Source: link:test-kernel-module[]
+
 Test that the Internet works:
 
 ....