Add conditional flag to change domain name construction for kerberos aut...

Add ability to correctly construct username for Kerberos auth for a host, that is already part of a Windows domain (and thus, only domain part of the host name must be appended to the username, rather than appending the FQDN of the host).

As an example, if the host name is **host.mydomain.com**: 
- in old implementation the username would be constructed as **user@host.mydomain.com** which is ok for single host and bad if host is part of domain;
- in this implementation, the username will be constructed as  **user@mydomain.com** if key _winrm-is-domain-member_=**true** and  as **user@host.mydomain.com** if key is set to **false**