Add script variables

The failover and switchover scripts need to be provided with credentials using which the scripts can access and make modifications to the affected servers. The scripts will use the same credentials as the MaxScale monitor does.

In the MaxScale configuration file it is possible to provide credentials for the monitor, to be used with all servers, and also servers specific monitor credentials.

A new script variable, e.g. CREDENTIALS could be introduced that would contain the credentials for all nodes.

script=failover.sh --slaves=$SLAVELIST --credentials=$CREDENTIALS

When executed, the command line would look like:

failover.sh --credentials=maxmon:maxpwd1@[192.168.0.201]:3306,maxmon:maxpwd2@[192.168.0.121]:3306

 --slaves=[192.168.0.201]:3306,[192.168.0.121]:3306