fix for the port param of dns_check function only accept int type input

[rongzeng54]

# python2.7
Python 2.7.14 (default, Jan 31 2018, 02:12:13)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-18)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import salt.utils
>>> salt.utils.dns_check('salt-master', int('4505'))
'x.x.x.x'
>>> salt.utils.dns_check('salt-master', '4505')
Attempt to resolve address 'mfsmaster' failed. Invalid or unresolveable address