Make build script exit early
Make build script exit early

Make build.sh exit early by updating to bash unofficial strict mode
defaults and exiting early if phing build fails.

This should make failure in the build process more clear and reduce
debugging efforts.

Additionallyi some other changes are made to foster stability of the
build script:

- Show composer version in build script

- Fix typo

- Clean phar file before build

p-makowski/n98-magerun2,p-makowski/n98-magerun2,p-makowski/n98-magerun2