Made Start-SshAgent faster

Don't store the SSH_AGENT_PID and SSH_AUTH_SOCK in [EnvironmentVariableTarget]::User) anymore. Moved to %TEMP%\.ssh

[EnvironmentVariableTarget]::User) user is painfully slow, because it notify other processes of the changed value, don't think that this is needed.
May cause a side effect i didn't thought of. Discussion?