Fixed link to a 'Cloud Tenant' from Instance Summary screen.

Added a check to fix undefined_method 'cloud_tenant ' error for an Amazon Instance.

https://bugzilla.redhat.com/show_bug.cgi?id=1146264
https://bugzilla.redhat.com/show_bug.cgi?id=1146265
Merge pull request #706 from h-kataria/fixed_link_to_tenant_from_amazon_instance_summary

Fixed link to a 'Cloud Tenant' from Instance Summary screen.