Fix the potential segmentation fault

Extral newline can trigger recovery segmentation fault
Test case:
host$ adb shell 'echo -en "--update_package=ota_update.zip\n--show_text\n\n" > /cache/recovery/command'
host$ adb reboot recovery

Change-Id: If1781c1f5ad94a273f1cb122b67cedd9fb562433
Signed-off-by: Jin Feng <jin88.feng@gmail.com>
recovery: use just the mount point instead of the full path

When resorting to using mount because a block device uses 'auto'
filesystem, we should use the mount point and not the full path.
This fixes an issue with nandroid to external sd on yuga.

Change-Id: Idbff944ea6d5af9112644c2ed46e23ea0a33e5ee
Merge "recovery: use just the mount point instead of the full path" into cm-10.1
Merge remote-tracking branch 'cm/cm-10.1' into cm-10.1