Made services installation optional during build

You can user `ENV` directive in Dockerfile to disable the installation
for some services or change `image/buildconfig`.

The flags are :

DISABLE_SSHD
DISABLE_CRON
DISABLE_SYSLOG

image/bin/enable_insecure_key

@@ -1,30 +0,0 @@
-#!/bin/bash
-set -e
-
-AUTHORIZED_KEYS=/root/.ssh/authorized_keys
-
-if [[ -e "$AUTHORIZED_KEYS" ]] && grep -q baseimage-docker-insecure-key "$AUTHORIZED_KEYS"; then
-	echo "Insecure key has already been added to $AUTHORIZED_KEYS."
-else
-	DIR=`dirname "$AUTHORIZED_KEYS"`
-	echo "Creating directory $DIR..."
-	mkdir -p "$DIR"
-	chmod 700 "$DIR"
-	chown root:root "$DIR"
-	echo "Editing $AUTHORIZED_KEYS..."
-	cat /etc/insecure_key.pub >> "$AUTHORIZED_KEYS"
-	echo "Success: insecure key has been added to $AUTHORIZED_KEYS"
-	cat <<-EOF
-
-		+------------------------------------------------------------------------------+
-		| Insecure SSH key installed                                                   |
-		|                                                                              |
-		| DO NOT expose port 22 on the Internet unless you know what you are doing!    |
-		|                                                                              |
-		| Use the private key below to connect with user root                         |
-		+------------------------------------------------------------------------------+
-
-	EOF
-	cat /etc/insecure_key
-	echo -e "\n\n"
-fi