[Tests] use -ex option during tests when possible

Relates to #1130

test/fast/Running "nvm unload" should unset all function and variables.

@@ -1,12 +1,13 @@
 #!/bin/sh
 
-fail () { echo $@ ; exit 1; }
+set -ex
+
+die () { echo $@ ; exit 1; }
 
 . ../../nvm.sh
 
-type nvm > /dev/null 2>&1 || fail "NVM not loaded"
+type nvm > /dev/null 2>&1 || die "nvm not loaded"
 
 nvm unload
 
-type nvm > /dev/null 2>&1 && fail "NVM not unloaded" || exit 0
-
+! type nvm > /dev/null 2>&1 || die "nvm not unloaded"