Return Fibre Channel port WWNs from a Windows host.

def _windows_wwns():
    '''
    Return Fibre Channel port WWNs from a Windows host.
    '''
    ps_cmd = r'Get-WmiObject -ErrorAction Stop ' \
             r'-class MSFC_FibrePortHBAAttributes ' \
             r'-namespace "root\WMI" | ' \
             r'Select -Expandproperty Attributes | ' \
             r'%{($_.PortWWN | % {"{0:x2}" -f $_}) -join ""}'
    ret = []
    cmd_ret = salt.modules.cmdmod.powershell(ps_cmd)
    for line in cmd_ret:
        ret.append(line.rstrip())
    return ret