Failures inside on_chroot do not stop the build

[tomas-c]

Most build scripts have "-e" option which is meant to make failed commands interrupt the script.

However, if any commands fail inside on_chroot call, the build still continues.

This seems a bit risky as you can only notice failures by carefully analysing build logs.

Replacing all instances of on_chroot with on_chroot -e fixes this.

[XECDesign]

Good idea. Does only changing https://github.com/RPi-Distro/pi-gen/blob/master/scripts/common#L91 to capsh --drop=cap_setfcap "--chroot=${ROOTFS_DIR}/" -- "-e $@" do the job?

[tomas-c]

It works if I move -e outside the quotes. I have created #219 with the necessary code changes.