esx: do not store escaped password in esxVI_Context.
    
    This patch fixes an issue where screenshot API call was failing when
    the esx/vcenter password contains special characters such as
    apostrophee. The reason for failures was that passwords were escaped
    for XML and stored in esxVI_Context which was then passed to raw CURL
    API calls where the password must be passed in original form to
    authenticate successfully. So this patch addresses this by storing
    original passwords in the esxVI_Context struct and escape only for
    esxVI_Login call.