scripts: Fix security_group.py handling of args and unknown commands
scripts: Fix security_group.py handling of args and unknown commands

Checks the args length, doesn't throw IndexError when no args
passed. Also logs to security_group.log when executed with no args or unknown
command.

Review: https://reviews.apache.org/r/9588
Reviewed-by: Rohit Yadav <0fa72ca37c4b5fa62675187ce32ea6c9f842fd52@apache.org>

Signed-off-by: Rohit Yadav <0fa72ca37c4b5fa62675187ce32ea6c9f842fd52@apache.org>

jcshen007/cloudstack,mufaddalq/cloudstack-datera-driver,mufaddalq/cloudstack-datera-driver,DaanHoogland/cloudstack,DaanHoogland/cloudstack,GabrielBrascher/cloudstack,DaanHoogland/cloudstack,GabrielBrascher/cloudstack,resmo/cloudstack,resmo/cloudstack,DaanHoogland/cloudstack,wido/cloudstack,wido/cloudstack,resmo/cloudstack,wido/cloudstack,resmo/cloudstack,wido/cloudstack,GabrielBrascher/cloudstack,resmo/cloudstack,wido/cloudstack,mufaddalq/cloudstack-datera-driver,GabrielBrascher/cloudstack,jcshen007/cloudstack,resmo/cloudstack,GabrielBrascher/cloudstack,jcshen007/cloudstack,mufaddalq/cloudstack-datera-driver,DaanHoogland/cloudstack,GabrielBrascher/cloudstack,jcshen007/cloudstack,resmo/cloudstack,GabrielBrascher/cloudstack,wido/cloudstack,wido/cloudstack,mufaddalq/cloudstack-datera-driver,jcshen007/cloudstack,DaanHoogland/cloudstack,jcshen007/cloudstack,DaanHoogland/cloudstack,mufaddalq/cloudstack-datera-driver,jcshen007/cloudstack