qapi: fix guardname generation

Fix a bug in handling dotted paths, and exclude directory prefixes
from generated guardnames to avoid odd/pseudo-random guardnames in
generated headers.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

scripts/qapi.py

@@ -200,6 +200,7 @@ def basename(filename):
     return filename.split("/")[-1]
 
 def guardname(filename):
-    if filename.startswith('./'):
-        filename = filename[2:]
-    return filename.replace("/", "_").replace("-", "_").split(".")[0].upper() + '_H'
+    guard = basename(filename).rsplit(".", 1)[0]
+    for substr in [".", " ", "-"]:
+        guard = guard.replace(substr, "_")
+    return guard.upper() + '_H'