qemu.tests: Install cygwin in windows guest

Add case for install cygwin env in windows guests.

change from v1:
   - Add cdrom letter replace to fit different system
   - typo fix and parameter adjust
change from v2:
   - cdrom check command change and the install command update

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Acked-by: Qingtang Zhou <qzhou@redhat.com>