Add return value when persist command does not return an error code on failure

Create a new python function "ovirt_store_config_retnum" to have it return
different error number consist with the different error case
In the shell script ovirt-functions.in, the "ovirt_store_config"
function will invoke the new python function "ovirt_store_config_retnum"
The ovirt_store_config will judge the error number from the ovirt_store_config_retnum

Change-Id: I014c41c9919cc9f8c260d85e0ef1a23ad17021a2
Signed-off-by: Changming Bai <baichm@linux.vnet.ibm.com>
Signed-off-by: lizhihui <zhihuili@linux.vnet.ibm.com>
Signed-off-by: MeiLiu <liumbj@linux.vnet.ibm.com>