Error checking in install script

[AdamBromiley]

Describe the bug
Half of the commands do not error check, so the install script will continue on error and appear as though the installation succeeded. It's a pretty important issue because this is the third time I've seen someone confused about why their install doesn't work/exist.

Expected behavior
An error message (which should be outputted by the failed command) and immediate exit with sufficient clean-up.