Handle vdevs with full paths

Index: util/getroot.c
===================================================================
--- util/getroot.c	2012-02-03 04:21:29.199249594 -0600
+++ util/getroot.c	2012-02-03 05:02:55.693211000 -0600
@@ -302,7 +301,10 @@
 		    devices = xrealloc (devices, sizeof (devices[0])
 					* devices_allocated);
 		  }
-		devices[ndevices++] = xasprintf ("/dev/%s", name);
+		if (name[0] == '/')
+		  devices[ndevices++] = xstrdup (name);
+		else
+		  devices[ndevices++] = xasprintf ("/dev/%s", name);
 	      }
 	    break;
 	  }