Multiple Fixes

[iainbrighton]

Description

• Fixed Set-NSHostname and Set-NSTimeZone update actions
  • Fixes #16
• Fixed ConvertTo-Json depth in PowerShell 5.1
  • Fixes #17
• Fixed filename rewrite issue in Add-NSSystemFile
  • Fixes #18
• Fixed DER certificate and certificate import without private key in Add-NSCertKeyPair
  • Fixes #21 and #22
• Add missing help examples

  How Has This Been Tested?

• Manually tested on NetScaler 10.5, 11.0 and 11.1

  Types of changes

• [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.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

Help tests are still failing but they now pass on:

• Add-NSCertKeyPair
• Add-NSSystemFile
• Set-NSHostName
• Set-NSTimeZone