CA-124248: Resolve EEXIST errors.

When attempting to manually recreate the symlinks which possess valid
dev-mapper entries, ignore EEXIST errors.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Chandrika Srinivasan <chandrika.srinivasan@citrix.com>

GitHub: closes #73 on xapi-project/sm