Potential conflict in generating_ssh_keys provided by azure-cli-core

[FumingZhang]

az feedback auto-generates most of the information requested below, as of CLI version 2.0.62

Describe the bug

When performing concurrent tests recently, we found that the generate_ssh_keys function provided by the cli core has potential concurrency conflicts.

In the existing implementation, when multiple processes try to create an ssh key, process A may have created a file but has not yet written key data, while process B reads an empty file at this time and obtains illegal empty key data.

In our module(acs/aks-preview), the example of calling this function is located in the validator.

For end users, this problem may also occur when users create multiple clusters (az aks create) at the same time and there is no ssh key that has been generated.

To Reproduce

Expected behavior

Environment summary

Additional context

A simple solution is to add a global lock to the generate_ssh_keys function.

[yonzhan]

@jiasli for awareness