skipped_host_aggregates regexp should allow hyphens

[Alvaro Uria]

Current regular expression allows: alphanumeric[,alphanumeric]

>>> import re
>>> s = "AZ-AGGR"
>>> regex = r'(\w+[,\w+]*)'
>>> re.findall(regex, s)
['AZ', 'AGGR']

However, there are host aggregates that may have hyphens or underscores.
>>> regex = r'([\w_-]+[,[\w_-]+]*)'
>>> re.findall(regex, s)
['AZ-AGGR']

[Alvaro Uria (aluria)]

updated regexp to r'([\w_-]+(?:,[\w_-]+)*)'