installation: filter padding from all tty output

This is both a bugfix and a generalization of #25168. In #25168, we attempted to filter padding
*just* from the debug output of `spack.util.executable.Executable` objects. It turns out we got it
wrong -- filtering the command line string instead of the arg list resulted in output like this:

```
==> [2021-08-05-21:34:19.918576] ["'", '/', 'b', 'i', 'n', '/', 't', 'a', 'r', "'", ' ', "'", '-', 'o', 'x', 'f', "'", ' ', "'", '/', 't', 'm', 'p', '/', 'r', 'o', 'o', 't', '/', 's', 'p', 'a', 'c', 'k', '-', 's', 't', 'a', 'g', 'e', '/', 's', 'p', 'a', 'c', 'k', '-', 's', 't', 'a', 'g', 'e', '-', 'p', 'a', 't', 'c', 'h', 'e', 'l', 'f', '-', '0', '.', '1', '3', '-', 'w', 'p', 'h', 'p', 't', 'l', 'h', 'w', 'u', 's', 'e', 'i', 'a', '4', 'k', 'p', 'g', 'y', 'd', 'q', 'l', 'l', 'i', '2', '4', 'q', 'b', '5', '5', 'q', 'u', '4', '/', 'p', 'a', 't', 'c', 'h', 'e', 'l', 'f', '-', '0', '.', '1', '3', '.', 't', 'a', 'r', '.', 'b', 'z', '2', "'"]
```

Additionally, plenty of builds output padded paths in other plcaes -- e.g., not just command
arguments, but in other `tty` messages via `llnl.util.filesystem` and other places. `Executable`
isn't really the right place for this.

This PR reverts the changes to `Executable` and moves the filtering into `llnl.util.tty`. There is
now a context manager there that you can use to install a filter for all output.
`spack.installer.build_process()` now uses this context manager to make `tty` do path filtering
when padding is enabled.

- [x] revert filtering in `Executable`
- [x] add ability for `tty` to filter output
- [x] install output filter in `build_process()`
- [x] tests

lib/spack/llnl/util/tty/__init__.py

@@ -5,6 +5,7 @@
 
 from __future__ import unicode_literals
 
+import contextlib
 import fcntl
 import os
 import struct
@@ -28,6 +29,7 @@
 _msg_enabled = True
 _warn_enabled = True
 _error_enabled = True
+_output_filter = lambda s: s
 indent = "  "
 
 
@@ -90,6 +92,18 @@ def error_enabled():
     return _error_enabled
 
 
+@contextlib.contextmanager
+def output_filter(filter_fn):
+    """Context manager that applies a filter to all output."""
+    global _output_filter
+    saved_filter = _output_filter
+    try:
+        _output_filter = filter_fn
+        yield
+    finally:
+        _output_filter = saved_filter
+
+
 class SuppressOutput:
     """Class for disabling output in a scope using 'with' keyword"""
 
@@ -166,13 +180,23 @@ def msg(message, *args, **kwargs):
     if _stacktrace:
         st_text = process_stacktrace(2)
     if newline:
-        cprint("@*b{%s==>} %s%s" % (
-            st_text, get_timestamp(), cescape(message)))
+        cprint(
+            "@*b{%s==>} %s%s" % (
+                st_text,
+                get_timestamp(),
+                cescape(_output_filter(message))
+            )
+        )
     else:
-        cwrite("@*b{%s==>} %s%s" % (
-            st_text, get_timestamp(), cescape(message)))
+        cwrite(
+            "@*b{%s==>} %s%s" % (
+                st_text,
+                get_timestamp(),
+                cescape(_output_filter(message))
+            )
+        )
     for arg in args:
-        print(indent + six.text_type(arg))
+        print(indent + _output_filter(six.text_type(arg)))
 
 
 def info(message, *args, **kwargs):
@@ -188,18 +212,29 @@ def info(message, *args, **kwargs):
     st_text = ""
     if _stacktrace:
         st_text = process_stacktrace(st_countback)
-    cprint("@%s{%s==>} %s%s" % (
-        format, st_text, get_timestamp(), cescape(six.text_type(message))
-    ), stream=stream)
+    cprint(
+        "@%s{%s==>} %s%s" % (
+            format,
+            st_text,
+            get_timestamp(),
+            cescape(_output_filter(six.text_type(message)))
+        ),
+        stream=stream
+    )
     for arg in args:
         if wrap:
             lines = textwrap.wrap(
-                six.text_type(arg), initial_indent=indent,
-                subsequent_indent=indent, break_long_words=break_long_words)
+                _output_filter(six.text_type(arg)),
+                initial_indent=indent,
+                subsequent_indent=indent,
+                break_long_words=break_long_words
+            )
             for line in lines:
                 stream.write(line + '\n')
         else:
-            stream.write(indent + six.text_type(arg) + '\n')
+            stream.write(
+                indent + _output_filter(six.text_type(arg)) + '\n'
+            )
 
 
 def verbose(message, *args, **kwargs):