spack load nonExistingPackage

does not return a non-zero return code to bash.

Expected Result

A non-zero return code and a message that the package does not exist

Actual Result

Zero return code and no message.

Steps to reproduce the issue

$ spack bootstrap
# default tcl modules
$ spack load nonExistingPackage

Information on your system

Debian 9.2
Spack 8ae50ae

ccing @alalazo