[common] handle all_logs when snap package is installed

When using `_outfile` in the first `Popen` and the command beig run
is a snap, then this will not work, and will not write to the file and
will be blank.

Dividing this into 2, and use `cat` as the second and grabbing it from
the PIPE solves this problem.

Resolves: sosreport#3683

Signed-off-by: Arif Ali <[email protected]>

sos/utilities.py

@@ -282,10 +282,17 @@ def _check_poller(proc):
             expanded_args.append(arg)
     if to_file:
         _output = open(to_file, 'w')
+        prep_p = Popen(expanded_args, shell=False, stdout=PIPE,
+                       stderr=STDOUT if stderr else PIPE,
+                       bufsize=-1, env=cmd_env, close_fds=True,
+                       preexec_fn=_child_prep_fn)
+        _stdin = prep_p.stdout
+        expanded_args = ['cat']
     else:
         _output = PIPE
+        _stdin = None
     try:
-        p = Popen(expanded_args, shell=False, stdout=_output,
+        p = Popen(expanded_args, stdin=_stdin, shell=False, stdout=_output,
                   stderr=STDOUT if stderr else PIPE,
                   bufsize=-1, env=cmd_env, close_fds=True,
                   preexec_fn=_child_prep_fn)