Replace use of depreciated function 'tmpnam.

Fix command line argument nesting.
Update comment for usage at comment line.

nongnu/system/build-image.scm

@@ -19,7 +19,7 @@
 ;;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 ;; Generate a bootable image with:
-;; $ ./nongnu/system/build-image.scm
+;; $ chmod +x build-image.scm && ./build-image.scm
 
 ; Searches through Scheme file for 'define and 'define* expressions
 ; such as (define <name> ... ) or (define (<name> ...) ...)
@@ -37,15 +37,20 @@
                exp)
               (#t (next (read port))))))))
 
-; Writes channel-list to a tmpfile defined by (tmpnam)
+; Writes channel-list to a tmpfile
 ; 'use-module is assumed to be needed, does not do anything if not used. TODO: remove assumption.
+; TODO: get mkstemp! to work (result of using it was a blank file)
 (define (make-tmp-channel channel-list)
-  (let ((tmpath (tmpnam)))
-    (call-with-output-file tmpath
+  (let loop ((tmpath (string-append "/tmp/guix-channel"
+                                    (number->string (random 1000000)))))
+    (cond ((file-exists? tmpath)
+           (loop (string-append "/tmp/guix-channel"
+                                (number->string (random 1000000)))))
+          (#t (call-with-output-file tmpath
                 (lambda (port)
                   (write '(use-modules (guix ci)) port)
                   (write channel-list port)))
-    tmpath))
+            tmpath))))
 
 ; Main function called when run at command line.
 ;   Parses "nongnu/system/install.scm" for channel definition
@@ -57,7 +62,7 @@
 ;     supports "--uncompressed" command line argument
 ;   If "--roll-back" is used as an argument, reverts guix pull
 ;   Returns #t if exit-code is 0, else returns #f
-(define (build-image . args)
+(define (build-image args)
   (let* ((image-type 'iso) ; todo: parse args for supported image types
          (image-label "nonguix-install")
          (channel-define-name '%channels)