autotest: simplify waitforbdev with new get_bdevs option

Rather than grepping through the get_bdevs output for a specific bdev's
name, use the new optional get_bdevs name parameter to check if the
specific bdev we want is available.

Change-Id: I14d82c81321d968c5553205af32d12c62533fb1c
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/375807
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

scripts/autotest_common.sh

@@ -202,7 +202,7 @@ function waitforbdev() {
 	rpc_py=$2
 
 	for ((i=1; i<=10; i++)); do
-		if [ ! -z "`$rpc_py get_bdevs | grep $bdev_name`" ]; then
+		if $rpc_py get_bdevs -b "$bdev_name" &>/dev/null; then
 			return 0
 		else
 			sleep 0.1