Adds Get-NSTimeZone and additional help tests

Description

Adds additional Help tests to ensure the correct command names are used in the examples
Fixed incorrect help command names in example help
Adds Get-NSTimeZone
Updates Set-NSTimeZone to accept pipeline input and return just the TimeZone. This might be classified as breaking change as the output has changed?
How Has This Been Tested?

Manually tested on NetScaler 11.0 and 11.1

[x] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)
Checklist:
[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[x] All new and existing tests passed.