Add --print-stacktrace-exception argument to pants invocations in ci.sh

When the build fails in ci, the stacktrace is suppressed by default. This change tacks on the --print-exception-stacktrace to each invocation of pants. (except for during the building of the distribution - it doesn't work then.)

Testing Done:
CI is running at https://travis-ci.org/pantsbuild/pants/builds/33585119

Bugs closed: 524

Reviewed at https://rbcommons.com/s/twitter/r/942/