Final async termination & few random fixes

- changed find_and_terminate_instance so inst_sem does not need to be
  held, also removed frivolous parameter to it
- moved shutdown in monitoring_thread into another thread, to avoid
  deadlock and timeouts
- removed ncStartNetwork invocation from CC, which has been a no-op on
  KVM and VMware back-ends for a while already
- moved check_device() to remove a false negative error in the log
- re-added axis2_stub_free, to please valgrind
- excluding SIGTERM and KILL from message 'BUG: child process... did not exit cleanly'
- avoiding 'downloaded -nan% of' in the log

Fixes EUCA-6124