fixed filebeat_ssl_key_file issue and a typo

[tdac]

When setting filebeat_ssl_key_file in group_vars - I was getting this strange error:

The conditional check 'filebeat_ssl_key_file' failed. 
The error was: error while evaluating conditional (filebeat_ssl_key_file): 'filebeat' is undefined
The error appears to have been in 'tasks/config.yml': line 11, column 3

This was resolved by checking the variables with 'is defined' (ansible 2.2.1.0 - ubuntu 16.04)

Also fixed a typo... :-)