agent: Reported MAC on Windows now the same as on Linux

Reporting of the MAC differs between linux and Windows guest operating
systems. The windows operating system reports it separated by dashes '-'.
This changeset will replace those dashes with colons ':'

Change-Id: Id19a8944025ee22d82a57b99fe4ba1c4315c27e9
Bug-Url: https://bugzilla.redhat.com/908761
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>