ci: add github workflow

cyrus-imapd has been relying on Travis CI for builds. And Travis CI
has been pretty unreliable for our use-case as we keep running out of
'free OSS credits'.
This commit adds support for Github Actions for builds.

While most of what we did with Travis worked with Actions, a minor
change in the how cassandane stops processes was also needed and is a
part of this commit. The change was to use `stop_command()` method
instead of `_stop_pid()` method directly, making sure that a
`waitpid()` call is made after a `kill()`.

Signed-off-by: Partha Susarla <mail@spartha.org>

.github/workflows/main.yml

@@ -0,0 +1,39 @@
+name: Cyrus IMAP CI
+
+on:
+  push:
+  pull_request:
+    branches:
+      - master
+      - main
+      - cyrus-imapd-3.6
+      - cyrus-imapd-3.4
+      - cyrus-imapd-3.2
+      - cyrus-imapd-3.0
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+        image: cyrusimapdocker/cyrus-buster:latest
+        options: --sysctl net.ipv6.conf.all.disable_ipv6=0
+    steps:
+    - uses: actions/checkout@v3
+    - name: configure and build
+      run: |
+        ./tools/build-with-cyruslibs.sh
+    - name: update jmap test suite
+      run: |
+        cd /srv/JMAP-TestSuite.git
+        git fetch
+        git checkout origin/master
+        git clean -f -x -d
+        cpanm --installdeps .
+        cd -
+    - name: run cassandane
+      run: |
+        cd cassandane
+        cp -af cassandane.ini.dockertests cassandane.ini
+        chown cyrus:mail cassandane.ini
+        make
+        setpriv --reuid=cyrus --regid=mail --clear-groups --inh-caps='-chown,-dac_override,-dac_read_search,-fowner,-fsetid,-kill,-setgid,-setuid,-setpcap,-linux_immutable,-net_bind_service,-net_broadcast,-net_admin,-net_raw,-ipc_lock,-ipc_owner,-sys_module,-sys_rawio,-sys_chroot,-sys_ptrace,-sys_pacct,-sys_admin,-sys_boot,-sys_nice,-sys_resource,-sys_time,-sys_tty_config,-mknod,-lease,-audit_write,-audit_control,-setfcap,-mac_override,-mac_admin,-syslog,-wake_alarm,-block_suspend,-audit_read,-cap_38,-cap_39,-cap_40' ./testrunner.pl -f pretty -j 4
+        cd -

cassandane/Cassandane/Instance.pm

@@ -1533,7 +1533,7 @@ sub stop
     {
         my $pid = $self->_read_pid_file($name);
         next if (!defined $pid);
-        _stop_pid($pid)
+        $self->stop_command($pid)
             or push @errors, "Cannot shut down $name pid $pid";
     }
     # Note: no need to reap this daemon which is not our child anymore