Tacacs, Maximum server limit

[Vignesh1405]

Issue Description: There is no limit on the number of Tacacs servers that can be added as host.
Root-Cause: A limit on the Number of Tacacs servers can that be added was not set.
What I did: added a limit as 8 on the number of Tacacs servers that can be added

What I did

I Have added a limit as 8 on the number of Tacacs servers that can be configured.

How I did it

Each time a new server is added, first it is checked weather the server address already exists, or else the number of tacacs servers already configured is checked. it the number is equal to eight, then further processing is stopped.

How to verify it

Configure eight Tacacs Servers. try to configure one more, the error message will be displayed saying "Maximum of 8 can be configured"

Previous command output (if the output of a command-line utility has changed)

NA

New command output (if the output of a command-line utility has changed)

NA

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