tests: Do not occlude subshell error codes when used as input to the test command

When using the output of a subshell as input, its error code is ignored in
the context of "set -e". Many test scripts use grub-shell in a subshell with
output used as an argument to the test command to test for expected output.
Refactor these tests so that the subshell output goes to a shell variable,
so that if the subshell errors the script will immediately exit with an
error code.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

tests/ohci_test.in

@@ -41,7 +41,12 @@ echo "hello" > "$outfile"
 
 tar cf "$imgfile" "$outfile"
 
-if [ "$(echo "nativedisk; source '(usb0)/$outfile';" | "${grubshell}" --qemu-opts="-device pci-ohci -drive id=my_usb_disk,file=$imgfile,if=none -device usb-storage,drive=my_usb_disk" | tail -n 1)" != "Hello World" ]; then
+v=$(echo "nativedisk; source '(usb0)/$outfile';" |
+    "${grubshell}" --qemu-opts="-device pci-ohci
+				-drive id=my_usb_disk,file=$imgfile,if=none
+				-device usb-storage,drive=my_usb_disk" |
+    tail -n 1)
+if [ "$v" != "Hello World" ]; then
    rm "$imgfile"
    rm "$outfile"
    exit 1