Resolve various build issues

[wjcarpenter]

The csng branch consistently failed to build for me when using the build-docker.sh script. I found 2 problems that were causing failures for me. After fixing those problems, the build went to completion.

1. Some scripts did not have execute permissions and were skipped because of that. I merely "chmod +x" to fix that.
2. When trying to sort out the loop devices for populating the boot and rootfs partitions, the rootfs step failed claiming there was no such file. I resolved that by adding a little more cushion in the "truncate" step.