Refactor bash test build system a bit

The basic idea here is to separate a few intertwined notions:

1. Not all "run bash tests" are "install tests"

2. Not all "run bash tests" use `tests/functional/init.sh`, or any
   pre-test initialization at all.

This will used in the next commit when we have a test that check unit
test golden master data.

Also, move our custom `PS4` from the test to the test runner, as it is
part of how we want to display the tests, not the test themselves.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

mk/run-test.sh

@@ -8,6 +8,7 @@ yellow=""
 normal=""
 
 test=$1
+init=${2-}
 
 dir="$(dirname "${BASH_SOURCE[0]}")"
 source "$dir/common-test.sh"
@@ -21,7 +22,9 @@ if [ -t 1 ]; then
 fi
 
 run_test () {
-    (init_test 2>/dev/null > /dev/null)
+    if [ -n "$init" ]; then
+        (init_test 2>/dev/null > /dev/null)
+    fi
     log="$(run_test_proper 2>&1)" && status=0 || status=$?
 }