Fixing issues with Import- and Save Context cmdlets

[markcowl]

Ensures that The token cache file is always created if possible, and that, if it cannot be, token cache loading works as well.

Description

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This checklist is used to make sure that common guidelines for a pull request are followed. You can find a more complete discussion of PowerShell cmdlet best practices here.

• I have read the contribution guidelines.
• If changes were made to any cmdlet, the XML help was regenerated using the platyPSHelp module.
• If any large changes are made to a service, they are reflected in the respective change log.

General Guidelines

• Title of the pull request is clear and informative.
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• The pull request does not introduce breaking changes (unless a major version change occurs in the assembly and module).

Testing Guidelines

• Pull request includes test coverage for the included changes.
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Cmdlet Signature Guidelines

• New cmdlets that make changes or have side effects should implement ShouldProcess and have SupportShouldProcess=true specified in the cmdlet attribute. You can find more information on ShouldProcess here.
• Cmdlet specifies OutputType attribute if any output is produced - if the cmdlet produces no output, it should implement a PassThru parameter.

Cmdlet Parameter Guidelines

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[markcowl]

signing run here: http://azuresdkci.cloudapp.net/view/1-AzurePowerShell/job/powershell-sign/1168/

on demand run: http://azuresdkci.cloudapp.net/view/1-AzurePowerShell/job/powershell-demand/1679/