(FM-5389) Add missing shared feature SNAC_SDK

[glennsarti]

Previously in commit 84f75b7 the feature list was extended however it missed
the SQL Native Client SDK. This commit adds the SNAC_SDK as a detectable and
installable feature. This commit also updates the README.

[glennsarti]

Note SQL Server 2016 (v13) installs SNAC and SNAC SDK v11 which equates to SQL Server 2012 e.g.

PS> puppet facts
...
    "sqlserver_features": {                  
      "SQL_2012": [                          
        "SNAC_SDK"                           
      ],                                     
      "SQL_2014": [                          
                                             
      ],                                     
      "SQL_2016": [                          
        "Conn",                              
        "SDK",                               
        "MDS",                               
        "BC",                                
        "DQC",                               
        "BOL",                               
        "DREPLAY_CTLR",                      
        "DREPLAY_CLT",                       
        "SQL_SHARED_MR",                     
        "IS"                                 
      ]                                      
    },                                       
...