Fix jenkins + linpack + bigmachine bug

launching 5-nodes for multinode testing; all 5 on a big machine
immediately attempt to run a linpack; this takes about 18-20secs - and
happens before a cloud forms.  Thus the first few tests timeout for
cloudsize being too small.
Stagger linpack tests.
Increase default stall-for-cloud timeout to 30sec
Move trap-cleanup code to before cluster is launched