containerize: ensure bootstrap images contain all system dependencies (#36818)

This also makes `spack bootstrap status` exit 1 if some dependency is missing

lib/spack/docs/bootstrapping.rst

@@ -32,9 +32,14 @@ can't be found. You can readily check if any prerequisite for using Spack is mis
 
    Spack will take care of bootstrapping any missing dependency marked as [B]. Dependencies marked as [-] are instead required to be found on the system.
 
+   % echo $?
+   1
+
 In the case of the output shown above Spack detected that both ``clingo`` and ``gnupg``
 are missing and it's giving detailed information on why they are needed and whether
-they can be bootstrapped. Running a command that concretize a spec, like:
+they can be bootstrapped. The return code of this command summarizes the results, if any
+dependencies are missing the return code is ``1``, otherwise ``0``. Running a command that
+concretizes a spec, like:
 
 .. code-block:: console
 
@@ -44,7 +49,7 @@ they can be bootstrapped. Running a command that concretize a spec, like:
    ==> Installing "clingo-bootstrap@spack%apple-clang@12.0.0~docs~ipo+python build_type=Release arch=darwin-catalina-x86_64" from a buildcache
    [ ... ]
 
-triggers the bootstrapping of clingo from pre-built binaries as expected.
+automatically triggers the bootstrapping of clingo from pre-built binaries as expected.
 
 Users can also bootstrap all the dependencies needed by Spack in a single command, which
 might be useful to setup containers or other similar environments:

lib/spack/spack/cmd/bootstrap.py

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 import os.path
 import shutil
+import sys
 import tempfile
 
 import llnl.util.filesystem
@@ -326,6 +327,7 @@ def _status(args):
     if missing:
         print(llnl.util.tty.color.colorize(legend))
         print()
+        sys.exit(1)
 
 
 def _add(args):