Minor install script improvements

* Install wget/curl in install_required_sw(), where all other required
  software is installed.
* Fix and standardize exit. install_rally.sh used three different ways
  to stop execution: abort(); die(); and err() + exit. die() has a
  strange usage pattern, and there are several places that use a
  two-argument die() which happily waits for stdin forever. In other
  cases we had unique and exciting hacks to get around die()'s
  strangeness. This fixes all of those, and makes everything either
  use abort() or die() (correctly).
* Fix inconsistent say()/echo usage. This eliminates the rarely-used
  say() function entirely.
* Quoted things that need quoted. Some other minor changes
  recommended by shellcheck.

Change-Id: I1a9d0b2ff5daba02998245d5c7e624f46bd2242a

tests/ci/test_install.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!/bin/sh -ex
 #
 # Copyright 2013: Mirantis Inc.
 # All Rights Reserved.