OCPBUGS-61373: Fix shellcheck issues in bootstrap

data/data/bootstrap/baremetal/files/usr/local/bin/build-metal3-env.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env sh
+#!/bin/bash
 
 set -euo pipefail
 

data/data/bootstrap/files/usr/local/bin/bootstrap-verify-api-server-urls.sh

@@ -10,7 +10,7 @@ function lookup_url() {
     unset IPS
     unset IP
     IPS=$(dig "${2}" +short)
-    if [[ ! -z "${IPS}" ]] ; then
+    if [[ -n "${IPS}" ]] ; then
         echo "Successfully resolved ${1} ${2}"
         return 0
     else

data/data/bootstrap/files/usr/local/bin/installer-gather.sh

@@ -6,7 +6,7 @@
 # Get target architecture
 arch=$(uname -m)
 
-if test "x${1}" = 'x--id'
+if test "${1}" = '--id'
 then
 	GATHER_ID="${2}"
 	shift 2

data/data/bootstrap/files/usr/local/bin/installer-masters-gather.sh

@@ -3,7 +3,7 @@
 # Get target architecture
 arch=$(uname -m)
 
-if test "x${1}" = 'x--id'
+if test "${1}" = '--id'
 then
 	GATHER_ID="${2}"
 	shift 2