build: Fail loudly if bash variables are unset, or a pipeline errors

These bash options increase the robustness of bash scripts, increasing
the chances that errors are spotted, instead of passing silently.

errexit was already enabled (by bash -e) if the scripts were invoked as

path/to/script.sh

However bash -e would not take effect if the script was invoked as

bash path/to/script.sh

The long form of the options is used to serve as an memory aide for
readers unfamiliar with bash options.

scripts/build.sh

@@ -1,4 +1,8 @@
-#!/bin/bash -e
+#!/bin/bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
 
 # Ted: contact me when you make any changes
 

scripts/build_image.sh

@@ -1,4 +1,9 @@
-#!/bin/bash -e
+#!/bin/bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
 SRC_DIR="$(dirname "${BASH_SOURCE[0]}")"
 export GOPATH="$SRC_DIR/.build_image_gopath"
 WORKPREFIX="$GOPATH/src/github.com/ava-labs/"

scripts/build_test.sh

@@ -1,4 +1,8 @@
-#!/bin/bash -e
+#!/bin/bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
 
 # Ted: contact me when you make any changes