Description of problem:
[RFE] Do not run auto attach available subscriptions to all systems - if there are no subscriptions at all

Version-Release number of selected component (if applicable):
* candlepin-0.8.19-1.el6sam.noarch
* candlepin-scl-1-5.el6_4.noarch
* candlepin-scl-quartz-2.1.5-5.el6_4.noarch
* candlepin-scl-rhino-1.7R3-1.el6_4.noarch
* candlepin-scl-runtime-1-5.el6_4.noarch
* candlepin-selinux-0.8.19-1.el6sam.noarch
* candlepin-tomcat6-0.8.19-1.el6sam.noarch
* elasticsearch-0.19.9-8.el6sat.noarch
* katello-candlepin-cert-key-pair-1.0-1.noarch
* katello-certs-tools-1.4.2-2.el6sat.noarch
* katello-cli-1.4.3-5.el6sat.noarch
* katello-cli-common-1.4.3-5.el6sat.noarch
* katello-common-1.4.3-6.el6sam_splice.noarch
* katello-configure-1.4.4-2.el6sat.noarch
* katello-glue-candlepin-1.4.3-6.el6sam_splice.noarch
* katello-glue-elasticsearch-1.4.3-6.el6sam_splice.noarch
* katello-headpin-1.4.3-6.el6sam_splice.noarch
* katello-headpin-all-1.4.3-6.el6sam_splice.noarch
* katello-selinux-1.4.4-2.el6sat.noarch
* thumbslug-0.0.32-1.el6sam.noarch
* thumbslug-selinux-0.0.32-1.el6sam.noarch

How reproducible:
Always

Steps to Reproduce:
1. Install SAM (Dont upload any subscriptions yet)
2. Subscribe and register few clients
3. Navigate to Systems page
4. Click "Auto-attach available subscriptions to all systems"

Actual results:
A success message shown saying all the clients are successfully auto attached

Expected results:
A user message showing there are no subscriptions to auto attach.

Additional info:
Similarly, if a user attempts to click "Auto-attach available subscriptions to all systems" without registering any systems - display a user message showing that there are no systems to auto attach.