ci: [win] Fix OpenSSL build, cleanup Conan, AppVeyor

[digitalcircuit]

In short

• Fix OpenSSL package name to openssl
  • Conan renamed their OpenSSL package
• Switch to Python 3 for Conan
  • Not required yet, but avoids future breakages (Python 2 is not supported)
  • Getting Python 3 in PATH is a bit wonky
• Build OpenSSL from source for x86 (32-bit)
  • Conan no longer seems to provide precompiled 32-bit builds
  • Cache results on AppVeyor to speed up future builds
• Stop Windows build process early if build fails
  • Easier to notice error messages
• Fix Windows Makefile for OpenSSL version 1.1.x
  • Handle OpenSSL 1.1.x renaming .lib files
  • Added more informative OpenSSL checks

Commits are intentionally split up for easier reference in the future. However, if preferred, they can still be squashed.

Criteria	Rank	Reason
Impact	★★☆ 2/3	Fixes Windows AppVeyor builds, upgrades OpenSSL
Risk	★★☆ 2/3	Switches Windows to OpenSSL 1.1.x, uses space in AppVeyor build cache
Intrusiveness	★☆☆ 1/3	Windows Makefile and CI, shouldn't interfere with other pull requests

Details

OpenSSL upgrade 1.0.x → 1.1.x

This is a significant upgrade to OpenSSL which includes changes to the Windows build process. Conan's OpenSSL package renamed ssleay32.lib into libssl.lib and libeay32.lib into libcrypto.lib. This PR updates makefile.win in a backwards-compatible way, using the newer file names if available, otherwise using the older paths.

The newer OpenSSL version might also impact Fuzzball's usage. Basic testing showed the TLS port as still working, but more thorough testing could be done.

Conan also renamed OpenSSL to openssl, which needed fixing in conanfile.txt.

Python 2 → Python 3

Python 2 technically still works, but is no longer supported. Unfortunately, it's a bit more difficult to access Python 3 on AppVeyor, so the Python 3 Scripts folder is determined at runtime and added to PATH.

Examples

Improved build failure handling

Before, the build error might be buried in the log file. Now, it shows up right after the build process.

Microsoft (R) Program Maintenance Utility Version 14.29.30133.0
Copyright (C) Microsoft Corporation.  All rights reserved.

[makefile.win] OpenSSL directory OPENSSLDIR not specified, assuming default
[makefile.win] Selected OpenSSL path: C:\projects\fuzzball/bin\lib\vc
[makefile.win] Using OpenSSL library names libcrypto.lib and libssl.lib
C:\projects\fuzzball/makefile.win(65) : fatal error U1050: TESTING BUILD PROCESS
Stop.
Build command exit code not zero: 2
Could not compile Fuzzball, build failed

Tested by inserting !ERROR TESTING BUILD PROCESS into makefile.win after the OpenSSL path logic.

AppVeyor Conan package caching

Once merged and built, the AppVeyor build cache should persist the OpenSSL build, resulting in faster future builds.

[...]
Restoring build cache
Cache 'C:\Users\Appveyor\.conan' - Restored
Running Install scripts

[...]

Version ranges solved
    Version range '~=1.1.1l' required by 'conanfile.txt' resolved to 'openssl/1.1.1l' in local cache
conanfile.txt: Installing package
Requirements
    openssl/1.1.1l from 'conancenter' - Cache
Packages
    openssl/1.1.1l:7b67ea8a8298b2c22e3896c8cb83cc30002fb75b - Cache
Cross-build from 'Windows:x86_64' to 'Windows:x86'
Installing (downloading, building) binaries...
openssl/1.1.1l: Already installed!
conanfile.txt: Generator txt created conanbuildinfo.txt
conanfile.txt: Aggregating env generators
conanfile.txt: Generated conaninfo.txt
[...]

Screenshots

Fuzzball running on AppVeyor with OpenSSL 1.1.1l, TLSv1.3

Though not shown in the screenshot, Fuzzball's welcome message shows and commands work. The source code commit hash does not match exactly as I had to push a modified commit to enable AppVeyor RDP login.