improve debug via _CLOUD_INIT_SAVE_STDIN and _CLOUD_INIT_SAVE_STDOUT

This does 2 things:
 a.) fixes broken logic in 'close_stdin'
     previously _CLOUD_INIT_SAVE_STDIN had to be set to false to
     preserve stdin.  "save_stdin" should be true to indicate it
     should be saved.

The net result is that you can stuff just add
 import pdb; pdb.set_trace()
to code, and then run something like:
 sudo _CLOUD_INIT_SAVE_STDIN=1 _CLOUD_INIT_SAVE_STDOUT=1 \
   cloud-init single --name=mounts --frequency=always

And enter the debugger even if you had a 'output' that would redirect
stdin/out by default, like:
   output: {all: '| tee -a /var/log/cloud-init-output.log'}

1 files changed, 12 insertions, 3 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index 23b67d48..6eb2a10e 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -406,7 +406,16 @@ def fixup_output(cfg, mode):
 #
 #   with a '|', arguments are passed to shell, so one level of
 #   shell escape is required.
+#
+#   if _CLOUD_INIT_SAVE_STDOUT is set in environment to a non empty and true
+#   value then output input will not be closed (useful for debugging).
+#
 def redirect_output(outfmt, errfmt, o_out=None, o_err=None):
+
+    if is_true(os.environ.get("_CLOUD_INIT_SAVE_STDOUT")):
+        LOG.debug("Not redirecting output due to _CLOUD_INIT_SAVE_STDOUT")
+        return
+
     if not o_out:
         o_out = sys.stdout
     if not o_err:
@@ -853,10 +862,10 @@ def close_stdin():
     reopen stdin as /dev/null so even subprocesses or other os level things get
     /dev/null as input.
 
-    if _CLOUD_INIT_SAVE_STDIN is set in environment to a non empty or '0' value
-    then input will not be closed (only useful potentially for debugging).
+    if _CLOUD_INIT_SAVE_STDIN is set in environment to a non empty and true
+    value then input will not be closed (useful for debugging).
     """
-    if is_false(os.environ.get("_CLOUD_INIT_SAVE_STDIN")):
+    if is_true(os.environ.get("_CLOUD_INIT_SAVE_STDIN")):
         return
     with open(os.devnull) as fp:
         os.dup2(fp.fileno(), sys.stdin.fileno())