Merge branch 'ps/ci-gitlab'

Add support for GitLab CI.

* ps/ci-gitlab:
  ci: add support for GitLab CI
  ci: install test dependencies for linux-musl
  ci: squelch warnings when testing with unusable Git repo
  ci: unify setup of some environment variables
  ci: split out logic to set up failed test artifacts
  ci: group installation of Docker dependencies
  ci: make grouping setup more generic
  ci: reorder definitions for grouping functions

diff --cc ci/lib.sh
Simple merge

diff --cc t/lib-httpd.sh
index 03493ee72bb8658a29ca11dcccb6980f40dc312f,9ea74927c4015d3d20ee946ded02b73b1775fd6e..d83bafeab32d40d6fd373e084757221ac7181d06
--- 1/t/lib-httpd.sh
--- 2/t/lib-httpd.sh
+++ b/t/lib-httpd.sh
@@@ -76,9 -68,9 +76,10 @@@ for DEFAULT_HTTPD_MODULE_PATH in '/usr/
                                 '/usr/lib64/httpd/modules' \
                                 '/usr/lib/httpd/modules' \
                                 '/usr/libexec/httpd' \
 -                               '/usr/lib/apache2'
++                               '/usr/lib/apache2' \
 +                               "${DETECTED_HTTPD_ROOT:+${DETECTED_HTTPD_ROOT}/modules}"
  do
 -      if test -d "$DEFAULT_HTTPD_MODULE_PATH"
 +      if test -n "$DEFAULT_HTTPD_MODULE_PATH" && test -d "$DEFAULT_HTTPD_MODULE_PATH"
        then
                break
        fi