Check that the mount directory exists

src/freedombone-prep

 
 function show_help {
     echo ''
-    echo 'freedombone-prep -d [microSD device] --ip [BBB LAN IP address] --iprouter [Router LAN IP address]'
+    echo 'freedombone-prep -d [microSD device] --ip [BBB LAN IP address] --iprouter [Router LAN IP address] --mount [mount directory]'
     echo ''
     echo 'See the manpage for more details'
     echo ''
   exit 0
 fi
 
+if [ ! -d $MICROSD_MOUNT_POINT ]; then
+    echo "The mount directory $MICROSD_MOUNT_POINT does not exist."
+    echo 'Use the --mount option to specify where the microSD gets mounted to.'
+    exit 67563
+fi
+
 while [[ $# > 1 ]]
 do
 key="$1"
     fi
 fi
 
+if [ ! -d $MICROSD_MOUNT_POINT/BOOT ]; then
+    echo "The boot partition $MICROSD_MOUNT_POINT/BOOT was not found."
+    exit 67857
+fi
+
+if [ ! -d $MICROSD_MOUNT_POINT/rootfs ]; then
+    echo "The rootfs partition $MICROSD_MOUNT_POINT/rootfs was not found."
+    exit 65688
+fi
+
 $SUDO cp $MICROSD_MOUNT_POINT/BOOT/bbb-uEnv.txt $MICROSD_MOUNT_POINT/BOOT/uEnv.txt
 
 $SUDO sed -i 's/iface eth0 inet dhcp/iface eth0 inet static/g' $MICROSD_MOUNT_POINT/rootfs/etc/network/interfaces