boxes: Update lxc-template to use a file lock around rootfs extraction

boxes/common/lxc-template

@@ -106,8 +106,24 @@ fi
 # Unpack the rootfs
 echo "Unpacking the rootfs"
 
-mkdir -p ${LXC_ROOTFS}
-(cd ${LXC_ROOTFS} && tar xfz ${LXC_TARBALL} --strip-components=2)
+
+(
+    flock -x 200
+    if [ $? -ne 0 ]; then
+        echo "Cache repository is busy."
+        return 1
+    fi
+
+    mkdir -p ${LXC_ROOTFS}
+    (cd ${LXC_ROOTFS} && tar xfz ${LXC_TARBALL} --strip-components=2)
+    if [ $? -ne 0 ]; then
+        echo "Failed to extract rootfs"
+        return 1
+    fi
+
+    return 0
+
+) 200>/var/lock/subsys/lxc
 
 mkdir -p ${LXC_ROOTFS}/dev/pts/