Update CHANGELOG and release version for v0.16.2

CHANGELOG.md

+# v0.16.2 (2021-05-22)
+
+* Major performance improvement for `spack load` and other commands. (#23661)
+* `spack fetch` is now environment-aware. (#19166)
+* Numerous fixes for the new, `clingo`-based concretizer. (#23016, #23307,
+  #23090, #22896, #22534, #20644, #20537, #21148)
+* Supoprt for automatically bootstrapping `clingo` from source. (#20652, #20657
+  #21364, #21446, #21913, #22354, #22444, #22460, #22489, #22610, #22631)
+* Python 3.10 support: `collections.abc` (#20441)
+* Fix import issues by using `__import__` instead of Spack package importe.
+  (#23288, #23290)
+* Bugfixes and `--source-dir` argument for `spack location`. (#22755, #22348,
+  #22321)
+* Better support for externals in shared prefixes. (#22653)
+* `spack build-env` now prefers specs defined in the active environment.
+  (#21642)
+* Remove erroneous warnings about quotes in `from_sourcing_files`. (#22767)
+* Fix clearing cache of `InternalConfigScope`. (#22609)
+* Bugfix for active when pkg is already active error. (#22587)
+* Make `SingleFileScope` able to repopulate the cache after clearing it.
+  (#22559)
+* Channelflow: Fix the package. (#22483)
+* More descriptive error message for bugs in `package.py` (#21811)
+* Use package-supplied `autogen.sh`. (#20319)
+* Respect `-k/verify-ssl-false` in `_existing_url` method. (#21864)
+
+
 # v0.16.1 (2021-02-22)
 
 This minor release includes a new feature and associated fixes:

lib/spack/spack/__init__.py

@@ -5,7 +5,7 @@
 
 
 #: major, minor, patch version for Spack, in a tuple
-spack_version_info = (0, 16, 1)
+spack_version_info = (0, 16, 2)
 
 #: String containing Spack version joined with .'s
 spack_version = '.'.join(str(v) for v in spack_version_info)