Simplify test starting and stopping logic

Reduce the coupling of the different scripts.

make-testing  : Build the testing environment
start-testing : Start switches and guests
do-tests      : Run tests
stop-testing  : Stop switches and guests

testing/testing.conf

@@ -76,9 +76,6 @@ ENABLE_BUILD_UMLKERNEL="yes"
 ENABLE_BUILD_UMLROOTFS="yes"
 ENABLE_BUILD_HOSTCONFIG="yes"
 ENABLE_BUILD_UMLHOSTFS="yes"
-ENABLE_START_TESTING="yes"
-ENABLE_DO_TESTS="no"
-ENABLE_STOP_TESTING="no"
 
 ##############################################################
 # If set to "yes" only the tests stated at $SELECTEDTESTS