Wait for devices before checking that raid exists (#424)

If devices were already part of existing raid, kernel could build the
raid automatically. In this case we can't create the new one with mdadm.

Also use the right name when performing check that device is already attached.

runtime/opt/taupage/init.d/10-prepare-disks.py

@@ -290,7 +290,9 @@ def iterate_mounts(region, config, max_tries=12, wait_time=5):
 def handle_ebs_volumes(region, ebs_volumes):
     ec2 = ec2_client(region)
     for device, name in ebs_volumes.items():
-        if os.path.exists(device):
+        # /dev/sda is renamed into /dev/xvda
+        xv_device = device.replace('/dev/sd', '/dev/xvd')
+        if os.path.exists(device) or os.path.exists(xv_device):
             logging.info("Device already exists %s", device)
         else:
             attach_volume(ec2, find_volume(ec2, name), device)
@@ -317,11 +319,7 @@ def create_raid_device(raid_device, raid_config, max_tries=12, wait_time=5):
                 "--create", raid_device,
                 "--run",
                 "--level=" + str(raid_level),
-                "--raid-devices=" + str(num_devices)]
-        # Give devices some time to be available in case they were recently attached
-        for device in devices:
-            wait_for_device(device)
-            call.append(device)
+                "--raid-devices=" + str(num_devices)] + devices
 
         tries = 0
         while True:
@@ -348,6 +346,10 @@ def create_raid_device(raid_device, raid_config, max_tries=12, wait_time=5):
 
 def handle_raid_volumes(raid_volumes):
     for raid_device, raid_config in raid_volumes.items():
+        # Give devices some time to be available in case they were recently attached
+        for device in raid_config.get("devices", []):
+            wait_for_device(device)
+
         if raid_device_exists(raid_device):
             logging.info("%s already exists", raid_device)
         else: