vdsm: fix dmidecode parsing

There is a version of dmidecode reported print #-prefixed comments, this
patch discards these lines.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1109342
Change-Id: I50493c5f77f59c5bdceac2a6e8223e8ccae75b09
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>