Fix building on Ubuntu

1) /bin/sh is not /bin/bash, so build.sh needs to explictly use /bin/bash
2) dash's echo does not support \x, but it does support \0 (since dash is
   /bin/sh, it gets used by Makefiles).

Makefile

-NO_COLOR=\x1b[0m
-OK_COLOR=\x1b[32;01m
-ERROR_COLOR=\x1b[31;01m
-WARN_COLOR=\x1b[33;01m
+NO_COLOR=\033[0m
+OK_COLOR=\033[32;01m
+ERROR_COLOR=\033[31;01m
+WARN_COLOR=\033[33;01m
 
 all:
 	@mkdir -p bin/

scripts/build.sh

-#!/bin/sh
+#!/bin/bash
 set -e
 
 NO_COLOR="\x1b[0m"
@@ -15,12 +15,12 @@ DIR="$( cd -P "$( dirname "$SOURCE" )/.." && pwd )"
 cd $DIR
 
 # Compile the main Packer app
-echo "${OK_COLOR}--> Compiling Packer${NO_COLOR}"
+echo -e "${OK_COLOR}--> Compiling Packer${NO_COLOR}"
 go build -v -o bin/packer .
 
 # Go over each plugin and build it
 for PLUGIN in $(find ./plugin -mindepth 1 -maxdepth 1 -type d); do
     PLUGIN_NAME=$(basename ${PLUGIN})
-    echo "${OK_COLOR}--> Compiling Plugin: ${PLUGIN_NAME}${NO_COLOR}"
+    echo -e "${OK_COLOR}--> Compiling Plugin: ${PLUGIN_NAME}${NO_COLOR}"
     go build -v -o bin/packer-${PLUGIN_NAME} ${PLUGIN}
 done