Fix performance regression with spack mirror create --all (#32005)

This PR fixes the performance regression reported in #31985 and a few
other issues found while refactoring the spack mirror create command.

Modifications:

* (Primary) Do not require concretization for
  `spack mirror create --all`
* Forbid using --versions-per-spec together with --all
* Fixed a few issues when reading specs from input file (specs were
  not concretized, command would fail when trying to mirror
  dependencies)
* Fix issue with default directory for spack mirror create not being
  canonicalized
* Add more unit tests to poke spack mirror create
* Skip externals also when mirroring environments
* Changed slightly the wording for reporting (it was mentioning
  "Successfully created" even in presence of errors)
* Fix issue with colify (was not called properly during error
  reporting)

lib/spack/llnl/util/lang.py

@@ -13,7 +13,7 @@
 import sys
 import traceback
 from datetime import datetime, timedelta
-from typing import List, Tuple
+from typing import Any, Callable, Iterable, List, Tuple
 
 import six
 from six import string_types
@@ -977,6 +977,31 @@ def enum(**kwargs):
     return type("Enum", (object,), kwargs)
 
 
+def stable_partition(
+    input_iterable,  # type: Iterable
+    predicate_fn,  # type: Callable[[Any], bool]
+):
+    # type: (...) -> Tuple[List[Any], List[Any]]
+    """Partition the input iterable according to a custom predicate.
+
+    Args:
+        input_iterable: input iterable to be partitioned.
+        predicate_fn: predicate function accepting an iterable item
+            as argument.
+
+    Return:
+        Tuple of the list of elements evaluating to True, and
+        list of elements evaluating to False.
+    """
+    true_items, false_items = [], []
+    for item in input_iterable:
+        if predicate_fn(item):
+            true_items.append(item)
+            continue
+        false_items.append(item)
+    return true_items, false_items
+
+
 class TypedMutableSequence(MutableSequence):
     """Base class that behaves like a list, just with a different type.