package/mender: update rootfs parts in mender.conf

The configuration options (RootfsPartA/RootfsPartB) must
provide a valid path to a block devices.

Signed-off-by: Mirza Krak <mirza.krak@northern.tech>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 637352b50b622bb4c2f1a529dd7565d4e573d1a6)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mender/mender.conf

@@ -2,8 +2,8 @@
   "InventoryPollIntervalSeconds": 1800,
   "UpdatePollIntervalSeconds": 1800,
   "RetryPollIntervalSeconds": 300,
-  "RootfsPartA": "mmcblk0p2",
-  "RootfsPartB": "mmcblk0p3",
+  "RootfsPartA": "/dev/mmcblk0p2",
+  "RootfsPartB": "/dev/mmcblk0p3",
   "ServerCertificate": "/etc/mender/server.crt",
   "ServerURL": "https://docker.mender.io",
   "TenantToken": "dummy"