etc/rc: avoid flux module cmd --rank option

In preparation for dropping the flux module cmd --rank
option, stop using it in rc scripts.

When the target is "-r 0", just drop the argument since
that is the default.  When the target is something else,
use flux exec to accomplish the same thing.

etc/rc1

@@ -2,24 +2,27 @@
 
 pids=""
 
-flux module load -r all barrier
-flux module load -r 0  content-sqlite
-flux module load -r 0 kvs
-flux module load -r all -x 0 kvs
-flux module load -r all kvs-watch
-flux module load -r all job-info
-flux module load -r all aggregator
+flux exec -r all flux module load barrier
+
+flux module load content-sqlite
+
+flux module load kvs
+flux exec -r all -x 0 flux module load kvs
+flux exec -r all flux module load kvs-watch
+
+flux exec -r all flux module load job-info
+flux exec -r all flux module load aggregator
 
 flux hwloc reload & pids="$pids $!"
 
-flux module load -r 0 cron sync=hb
+flux module load cron sync=hb
 
-flux module load -r 0 userdb ${FLUX_USERDB_OPTIONS}
+flux module load userdb ${FLUX_USERDB_OPTIONS}
 
-flux module load -r all job-ingest
-flux module load -r 0 job-manager
-flux module load -r 0 job-exec
-flux module load -r 0 sched-simple
+flux exec -r all flux module load job-ingest
+flux module load job-manager
+flux module load job-exec
+flux module load sched-simple
 
 wait $pids
 

etc/rc3

@@ -12,28 +12,28 @@ for rcdir in $all_dirs; do
 done
 shopt -u nullglob
 
-flux module remove -r 0 sched-simple
-flux module remove -r 0 job-exec
-flux module remove -r 0 job-manager
-flux module remove -r all job-ingest
+flux module remove sched-simple
+flux module remove job-exec
+flux module remove job-manager
+flux exec -r all flux module remove job-ingest
 
 if PERSISTDIR=$(flux getattr persist-directory 2>/dev/null); then
     /bin/true; # XXX: nothing to persist?
 fi
 
-flux module remove -r 0 userdb
+flux module remove userdb
 
-flux module remove -r 0 cron
-flux module remove -r all aggregator
-flux module remove -r all barrier
+flux module remove cron
+flux exec -r all flux module remove aggregator
+flux exec -r all flux module remove barrier
 
-flux module remove -r all job-info
-flux module remove -r all kvs-watch
-flux module remove -r all -x 0 kvs
+flux exec -r all flux module remove job-info
+flux exec -r all flux module remove kvs-watch
+flux exec -r all -x 0 flux module remove kvs
 if test -n "$PERSISTDIR"; then
     flux kvs getroot >${PERSISTDIR}/kvsroot.final
     flux content flush
 fi
-flux module remove -r 0 kvs
-flux module remove -r 0 content-sqlite
+flux module remove kvs
+flux module remove content-sqlite