Add check that poudriere is not already running.

ansible/roles/poudriere/files/poudboot.bash

@@ -38,6 +38,8 @@ function build {
 }
 
 function cmd_start {
+    abort_if_jobs_running
+
     # Allow command failures without quitting the script because some
     # package sets might fail whereas others may succeed based on which
     # packages are in each set.