cmd/flux-version: add --remote option

If --remote option is given, connect to broker and
get 'version' attribute

Fixes flux-framework#1810

src/cmd/builtin/version.c

@@ -28,10 +28,26 @@
 
 static int cmd_version (optparse_t *p, int ac, char *av[])
 {
-    printf ("%s-%s\n", PACKAGE_NAME, PACKAGE_VERSION);
+    const char *version = PACKAGE_VERSION;
+
+    if (optparse_hasopt (p, "remote")) {
+        flux_t *h = builtin_get_flux_handle (p);
+        if (!h)
+            log_err_exit ("flux_open");
+        if (!(version = flux_attr_get (h, "version", NULL)))
+            log_err_exit ("flux_attr_get");
+    }
+
+    printf ("%s-%s\n", PACKAGE_NAME, version);
     return (0);
 }
 
+static struct optparse_option version_opts[] = {
+    { .name = "remote",  .key = 'r',  .has_arg = 0,
+      .usage = "Connect to flux broker for version", },
+      OPTPARSE_TABLE_END,
+};
+
 int subcommand_version_register (optparse_t *p)
 {
     optparse_err_t e;
@@ -41,7 +57,7 @@ int subcommand_version_register (optparse_t *p)
         NULL,
         "Display flux version information",
         0,
-        NULL);
+        version_opts);
     return (e == OPTPARSE_SUCCESS ? 0 : -1);
 }