add nosec to subprocess usage in launch_command
add nosec to subprocess usage in launch_command

this change will supress the warnings generated by bandit for the
subprocess usages. it also adds a TODO to investigate improving security
for the launch_command.

Change-Id: I1aa72d89922944af390d93adabfc979811056a84
Closes-Bug: 1552481

egafford/sahara,tellesnobrega/sahara,openstack/sahara,egafford/sahara,openstack/sahara,tellesnobrega/sahara