job-list: add nodelist hostlist to job_data

Problem: In the near future it'd be convenient to do calculations
on the job nodelist, but it often needs to be in a hostlist
data structure for processing.  We'd like to avoid converting the
nodelist to hostlist struct over and over again.

Add a field into the job_data struct to hold a cached version of the
nodelist in a hostlist struct.

Author: chu11

src/modules/job-list/job_data.c

@@ -35,6 +35,7 @@ void job_destroy (void *data)
         int save_errno = errno;
         free (job->ranks);
         free (job->nodelist);
+        hostlist_destroy (job->nodelist_hl);
         json_decref (job->annotations);
         grudgeset_destroy (job->dependencies);
         json_decref (job->jobspec);

src/modules/job-list/job_data.h

@@ -14,6 +14,7 @@
 #include <flux/core.h>
 #include <jansson.h>
 
+#include "src/common/libhostlist/hostlist.h"
 #include "src/common/libutil/grudgeset.h"
 #include "src/common/libczmqcontainers/czmq_containers.h"
 
@@ -54,6 +55,7 @@ struct job {
     int nnodes;
     char *ranks;
     char *nodelist;
+    struct hostlist *nodelist_hl; /* cache of nodelist in hl form */
     double expiration;
     int wait_status;
     bool success;