check_mssql_database.py - Seperate database connection from table name

[barosch78]

In a very old version of this script I was able to check the transactions per second for all databases over the virtual table name _Total because the database name was hardcoded to 'master'

SELECT * FROM sys.sysperfinfo WHERE counter_name='Transactions/sec' AND instance_name='_Total'

In the actual version this is not longer possible because the table and the database are the same.
I changed the script according to my needs. Maybe someone else will find this useful as well.

Greetings
Barosch