Move from .app.src to Makefile variables

This is the recommended way with Erlang.mk.

By default, the version is inherited from rabbitmq-server-release when
the source archive is created, or computed from git-describe(1) (see
`rabbitmq-components.mk`). One can override the version from the command
line by setting the `PROJECT_VERSION` variable.

[#130992027]

deps/rabbitmq_ct_helpers/Makefile

@@ -1,4 +1,5 @@
 PROJECT = rabbitmq_ct_helpers
+PROJECT_DESCRIPTION = Common Test helpers for RabbitMQ
 
 DEPS = rabbit_common proper
 

deps/rabbitmq_ct_helpers/rabbitmq-components.mk

@@ -5,6 +5,27 @@ ifeq ($(.DEFAULT_GOAL),)
 .DEFAULT_GOAL = all
 endif
 
+# PROJECT_VERSION defaults to:
+#   1. the version exported by rabbitmq-server-release;
+#   2. the version stored in `git-revisions.txt`, if it exists;
+#   3. a version based on git-describe(1), if it is a Git clone;
+#   4. 0.0.0
+
+PROJECT_VERSION = $(RABBITMQ_VERSION)
+
+ifeq ($(PROJECT_VERSION),)
+PROJECT_VERSION := $(shell \
+if test -f git-revisions.txt; then \
+	head -n1 git-revisions.txt | \
+	awk '{print $$$(words $(PROJECT_DESCRIPTION) version);}'; \
+else \
+	(git describe --dirty --abbrev=7 --tags --always --first-parent \
+	 2>/dev/null || echo rabbitmq_v0_0_0) | \
+	sed -e 's/^rabbitmq_v//' -e 's/^v//' -e 's/_/./g' -e 's/-/+/' \
+	 -e 's/-/./g'; \
+fi)
+endif
+
 # --------------------------------------------------------------------
 # RabbitMQ components.
 # --------------------------------------------------------------------