Fix API handler generator to support GET appropriately

This patch fixes the decorator for the API handler generator to add
methods correspond to HTTP GET for the single and multiple resources.

Change-Id: Ifffbb8f70390b9f543b0e267e681b86b9508432c
Signed-off-by: Taku Fukushima <tfukushima@midokura.com>
Merge "Fix API handler generator to support GET appropriately"