can fail with if a security group is specified in the location

[ahgittin]

i've got a location whose definition specifies securityGroup: universal

when i try to deploy clocker to it (using "Clocker with Calico" in clocker 1.1.0) it fails during pre-start when the JcloudsLocationSecurityGroupCustomizer is looking for the machine-group-specific security group.

it's arguably a bug in the security group customizer, that it should:

• skip customisation if the desired rules are already present
• if it can't find the security group wrap the exception in one which gives a better name