MFC r297986, r298017 to vdev_geom.c

r297986 | asomers | 2016-04-14 13:20:31 -0600 (Thu, 14 Apr 2016) | 6 lines

Update a debugging message in vdev_geom_open_by_guids for consistency with
similar messages elsewhere in the file.

r298017 | asomers | 2016-04-14 17:14:41 -0600 (Thu, 14 Apr 2016) | 8 lines

Add more debugging statements in vdev_geom.c

Log a debugging message whenever geom functions fail in vdev_geom_attach.
Printing these messages is controlled by vfs.zfs.debug