install_pmbootstrap: v3: set pmaports dir (MR 7)

In pmbootstrap v3, the --aports argument currently gets ignored in:
$ pmbootstrap --aports=.... init

As workaround, let pmbootstrap initialized with the default (which means
it clones pmaports to the default dir), and then change the config
afterwards to point to the pmaports dir we actually want to run CI in.

Related: pmb issue 2412
Related: pmb issue 2411

install_pmbootstrap.sh

@@ -118,3 +118,10 @@ if ! su pmos -c "yes '' | pmbootstrap \
 	exit 1
 fi
 echo ""
+
+# Workaround for pmb#2412: currently the pmaports_arg gets ignored in pmb v3,
+# so let pmbootstrap clone pmaports in the default dir during init, then change
+# the pmaports path to the one from the current merge request.
+if [ "$PMBOOTSTRAP_TAG" != "2.3.x" ] && [ -n "$pmaports_arg" ]; then
+	su - pmos -c "pmbootstrap config aports '$pmaports'"
+fi