test: move greenprint and redprint functions to shared_lib.sh

Since we're sharing functions between test scripts, move greenprint(),
the most rewritten function in the history of the project, to
shared_lib.sh and source it everywhere.

test/cases/container-embedding.sh

@@ -1,10 +1,6 @@
 #!/usr/bin/bash
 set -euxo pipefail
 
-# Colorful timestamped output.
-function greenprint {
-    echo -e "\033[1;32m[$(date -Isecond)] ${1}\033[0m"
-}
 
 source /usr/libexec/osbuild-composer-test/set-env-variables.sh
 source /usr/libexec/tests/osbuild-composer/shared_lib.sh