private static void isFilePresent(String keyFile) {
		File file = new File(keyFile);
		if (!file.exists()) {
			throw new IllegalArgumentException("The XD Private Key File ==> " + keyFile + " does not exist.");
		}
	}
Retrieves the private key from a file, so we can execute commands on the container.

@param fileName The location of the private key file
@return The private key
spring-xd-integration-test/src/main/java/org/springframework/xd/integration/util/ConfigUtil.java