container polling logic cleanup

luasrc/view/tasks/docker.htm

@@ -17,8 +17,8 @@ if not task_running then
     <%
     local util  = require "luci.util"
     local container_status = util.trim(util.exec(self.script_path.." status"))
-    local container_install = (string.len(container_status) > 0)
-    local container_running = container_status == "running"
+    local container_install = not string.match(container_status, " is not installed$")
+    local container_running = string.match(string.lower(container_status), "^up .* (seconds|minutes|hours)")
     if container_install then
     -%>
     <input class="btn cbi-button cbi-button-apply" type="button" value="<%:Upgrade%>/<%:Apply%>" onclick="cbi_submit(this, 'cbi.apply', 'upgrade')" />