Description of problem:
Content hosts -> Errata tab: Add helptext to inform Applicable errata cannot be applied

Version-Release number of selected component (if applicable):
Satellite-6.1.0-RHEL-6-20150217.0

How reproducible:
Always

Steps to Reproduce:
1. Upload a manifest, sync a repo (with errata)
2. Create multiple environments say Library -> QE
3. Create content view (cv3) and make sure Library has more errata than QE environment
4. Register a content host to QE environment

Actual results:
Go to Content host -> Errata tab
- 1. Select Current Environment (QE/cv3) - shows 'Installable errata'.
- 2. Select Previous Environment (Library/cv3) - shows 'Applicable errata'
- 3. Select Library Synced Content - shows 'Applicable errata'

For scenarios 2 and 3 above, I am not able to actually install errata as part of Incremental updates.  I learnt later that Incremental Updates can be applied only from Content -> 'Errata'

Expected results:
For scenarios 2 and 3 above, make it obvious to the user that these are not installed by
- Adding clear help text that this is view only and install of these errata can be done only from Content -> Errata page.
- greying out errata selection options
and anything else which is necessary

Additional info: