pmbootstrap aportgen: don't use CDN alpine mirror (MR 1963)

Use a deterministic mirror URL instead of CDN for aportgen. Otherwise we
may generate a pmaport that wraps an apk from Alpine (e.g. musl-armv7)
locally with one up-to-date mirror given by the CDN. But then the build
will fail if CDN picks an outdated mirror for CI or BPO.

pmb/aportgen/busybox_static.py

@@ -42,7 +42,7 @@ def generate(args, pkgname):
             pkgrel={pkgrel}
 
             _arch="{arch}"
-            _mirror="{args.mirror_alpine}"
+            _mirror="{pmb.config.aportgen_mirror_alpine}"
 
             url="http://busybox.net"
             license="GPL2"

pmb/aportgen/grub_efi.py

@@ -37,7 +37,7 @@ def generate(args, pkgname):
             pkgrel={pkgrel}
 
             _arch="{arch}"
-            _mirror="{args.mirror_alpine}"
+            _mirror="{pmb.config.aportgen_mirror_alpine}"
 
             pkgdesc="GRUB $_arch EFI files for every architecture"
             url="https://www.gnu.org/software/grub/"

pmb/aportgen/musl.py

@@ -47,7 +47,7 @@ def generate(args, pkgname):
             subpackages="musl-dev-{arch}:package_dev"
 
             _arch="{arch}"
-            _mirror="{args.mirror_alpine}"
+            _mirror="{pmb.config.aportgen_mirror_alpine}"
 
             url="https://musl-libc.org"
             license="MIT"

pmb/config/__init__.py

@@ -553,6 +553,12 @@ aportgen = {
     }
 }
 
+# Use a deterministic mirror URL instead of CDN for aportgen. Otherwise we may
+# generate a pmaport that wraps an apk from Alpine (e.g. musl-armv7) locally
+# with one up-to-date mirror given by the CDN. But then the build will fail if
+# CDN picks an outdated mirror for CI or BPO.
+aportgen_mirror_alpine = "http://dl-2.alpinelinux.org/alpine/"
+
 #
 # NEWAPKBUILD
 # Options passed through to the "newapkbuild" command from Alpine Linux. They