Enhance bash shebangs

installer/lxc-bootstrap

@@ -1,4 +1,4 @@
-#!/bin/bash -e
+#!/usr/bin/env bash -e
 #-e Causes bash script to exit if any of the installers
 #return with a non-zero return value.
 

installer/vagrant/centos.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Additional Repos
 yum install -y epel-release

installer/vagrant/debian.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 DEBIAN_FRONTEND=noninteractive apt-get -y install alsa-utils
 usermod -a -G audio vagrant