Add jupyter-refresh-kernelspecs command

* jupyter-kernelspec.el (jupyter-kernelspecs): Mention REFRESH
argument in documentation.
(jupyter-do-refresh-kernelspecs): New method that does the work of
refreshing the kernelspecs.
(jupyter-refresh-kernelspecs): New interactive command that calls the method.

* ob-jupyter.el (jupyter-do-refresh-kernelspecs): New method
definition for Org specific contexts.

closes #507

jupyter-kernelspec.el

@@ -137,12 +137,28 @@ why it isn't returning valid JSON."))))
     kernelspecs))
 
 (cl-defgeneric jupyter-kernelspecs (host &optional refresh)
-  "Return a list of kernelspecs on HOST.")
+  "Return a list of kernelspecs on HOST.
+If REFRESH is non-nil, then refresh the list of cached
+kernelspecs first.  Otherwise a cached version of the kernelspecs
+may be returned.")
 
 (cl-defmethod jupyter-kernelspecs ((host string) &optional refresh)
   (let ((default-directory host))
     (jupyter-available-kernelspecs refresh)))
 
+(cl-defmethod jupyter-do-refresh-kernelspecs ()
+  (jupyter-kernelspecs default-directory 'refresh))
+
+;;;###autoload
+(defun jupyter-refresh-kernelspecs ()
+  "Refresh the list of available kernelspecs.
+Execute this command if the kernelspecs seen by Emacs is out of
+sync with those specified on your system or notebook server."
+  (interactive)
+  (message "Refreshing kernelspecs...")
+  (jupyter-do-refresh-kernelspecs)
+  (message "Refreshing kernelspecs...done"))
+
 (defun jupyter-get-kernelspec (name &optional specs refresh)
   "Get the kernelspec for a kernel named NAME.
 If no kernelspec is found, return nil.  Otherwise return the

ob-jupyter.el

@@ -417,7 +417,7 @@ the host."
       (setq session (org-babel-read session)))
     (org-babel-jupyter-initiate-session-by-key session params)))
 
-;;;;  `org-babel-execute:jupyter'
+;;;; Helper functions
 
 ;;;###autoload
 (defun org-babel-jupyter-scratch-buffer ()
@@ -430,6 +430,17 @@ the host."
     (if buffer (pop-to-buffer buffer)
       (user-error "No source block at point"))))
 
+(cl-defmethod jupyter-do-refresh-kernelspecs (&context (major-mode org-mode))
+  (or (jupyter-org-when-in-src-block
+       (let* ((info (org-babel-get-src-block-info 'light))
+              (params (nth 2 info))
+              (session (org-babel-read (alist-get :session params))))
+         (when (file-remote-p session)
+           (jupyter-kernelspecs session 'refresh))))
+      (cl-call-next-method)))
+
+;;;;  `org-babel-execute:jupyter'
+
 (defvar org-bracket-link-regexp)
 
 (defun org-babel-jupyter-cleanup-file-links ()