Allow to update tftpd configuration

This patch reworks tftpd-hpa module to allow specify tftpd
configuration options like:
  username, directory, options

Change-Id: I4fbaa9a4149ca230008099aa29834a8f9de6449b
diff --git a/tests/pillar/server_single.sls b/tests/pillar/server_single.sls
index e6d8346..7c73b29 100644
--- a/tests/pillar/server_single.sls
+++ b/tests/pillar/server_single.sls
@@ -1,4 +1,10 @@
 tftpd_hpa:
   server:
     enabled: true
-
+    bind:
+      address: '0.0.0.0'
+      port: 69
+    username: 'root'
+    options:
+      - secure
+      - map-file: '/var/lib/tftproot/map-file'