docker: improve dev env

- abort docker scripts on error
- generate version in system tests
- build debian packages in docker
- add make clean target
- fix lint

system/t04_mirror/CreateMirror18Test_gold

@@ -1,5 +1,4 @@
 Downloading: http://ppa.launchpad.net/gladky-anton/gnuplot/ubuntu/dists/maverick/InRelease
-gpgv: can't allocate lock for '/home/runner/.gnupg/ppa.gpg'
 gpgv: Signature made Sun Jul 28 07:57:01 2024 UTC
 gpgv:                using RSA key 5BFCD481D86D5824470E469F9000B1C3A01F726C
 gpgv: Good signature from "Launchpad PPA for Anton Gladky"

system/t04_mirror/CreateMirror30Test_gold

@@ -1,4 +1,4 @@
-opengpg: failure opening keyring '/home/runner/.gnupg/aptlytest.gpg': open /home/runner/.gnupg/aptlytest.gpg: no such file or directory
+opengpg: failure opening keyring '${HOME}/.gnupg/aptlytest.gpg': open ${HOME}/.gnupg/aptlytest.gpg: no such file or directory
 
 Looks like your keyring with trusted keys is empty. You might consider importing some keys.
 Downloading: http://repo.aptly.info/system-tests/archive.debian.org/debian-archive/debian/dists/stretch/InRelease

system/t04_mirror/create.py

@@ -223,7 +223,8 @@ class CreateMirror18Test(BaseTest):
     }
 
     fixtureCmds = [
-        "gpg --no-default-keyring --keyring=ppa.gpg --keyserver=hkp://keyserver.ubuntu.com:80 --recv-keys 5BFCD481D86D5824470E469F9000B1C3A01F726C 02219381E9161C78A46CB2BFA5279A973B1F56C0"
+        "gpg --no-default-keyring --keyring=ppa.gpg --keyserver=hkp://keyserver.ubuntu.com:80 --recv-keys 5BFCD481D86D5824470E469F9000B1C3A01F726C 02219381E9161C78A46CB2BFA5279A973B1F56C0",
+        f"chmod 400 {os.path.join(os.environ['HOME'], '.gnupg/ppa.gpg')}"
     ]
     runCmd = "aptly mirror create -keyring=ppa.gpg mirror18 ppa:gladky-anton/gnuplot"