CLOUDSTACK-7355 - test_netscaler_configs.py uses hardcoded NetScaler credentials

Refactored code to use test_data instead of hardcoded NetScaler credentials
Refactored code to remove large scale duplication
Fixed some minor logic error in the existing tests

This patch has not added or removed any of the original test-cases.

Signed-off-by: SrikanteswaraRao Talluri <talluri@apache.org>