[minor] change the way AGTCONF and LOADERCONF are handled in Makefile

When building the mig-agent or mig-loader targets and specifying AGTCONF
or LOADERCONF, configuration.go in the relevant directory is replaced by
the referenced configuration. If AGTCONF or LOADERCONF is not
overridden, the configuration is not replaced.

This can lead to inconsistent build results, as by building for example
the mig-agent target a second time with no AGTCONF, the replaced
configuration.go will be retained.

This changes this behavior, so configuration.go is always replaced with
the configuration files in conf/, unless the Makefile configuration
variable has been overridden.

Makefile

@@ -58,8 +58,8 @@ endif
 PREFIX		:= /usr/local/
 DESTDIR		:= /
 BINDIR		:= bin/$(OS)/$(ARCH)
-AGTCONF		:= mig-agent/configuration.go
-LOADERCONF	:= mig-loader/configuration.go
+AGTCONF		:= conf/mig-agent-conf.go.inc
+LOADERCONF	:= conf/mig-loader-conf.go.inc
 MSICONF		:= mig-agent-installer.wxs
 SIGNFLAGS	:=
 
@@ -93,9 +93,9 @@ create-bindir:
 mig-agent: create-bindir
 	echo building mig-agent for $(OS)/$(ARCH)
 	if [ ! -r $(AGTCONF) ]; then echo "$(AGTCONF) configuration file does not exist" ; exit 1; fi
-	# test if the agent configuration variable contains something different than the default value
-	# and if so, replace the link to the default configuration with the provided configuration
-	if [ $(AGTCONF) != "mig-agent/configuration.go" ]; then rm mig-agent/configuration.go; cp $(AGTCONF) mig-agent/configuration.go; fi
+	# Copy the configuration referenced by AGTCONF into place; you can override this variable
+	# to specify a built-in configuration to use other than conf/mig-agent-conf.go.inc
+	cp $(AGTCONF) mig-agent/configuration.go
 	$(GO) build $(GOOPTS) -o $(BINDIR)/mig-agent-$(BUILDREV)$(BINSUFFIX) $(GOLDFLAGS) mig.ninja/mig/mig-agent
 	ln -fs "$$(pwd)/$(BINDIR)/mig-agent-$(BUILDREV)$(BINSUFFIX)" "$$(pwd)/$(BINDIR)/mig-agent-latest"
 	[ -x "$(BINDIR)/mig-agent-$(BUILDREV)$(BINSUFFIX)" ] || (echo FAILED && false)
@@ -119,9 +119,9 @@ mig-action-generator: create-bindir
 
 mig-loader: create-bindir
 	if [ ! -r $(LOADERCONF) ]; then echo "$(LOADERCONF) configuration file does not exist" ; exit 1; fi
-	# test if the loader configuration variable contains something different than the default value
-	# and if so, replace the link to the default configuration with the provided configuration
-	if [ $(LOADERCONF) != "mig-loader/configuration.go" ]; then rm mig-loader/configuration.go; cp $(LOADERCONF) mig-loader/configuration.go; fi
+	# Copy the configuration referenced by LOADERCONF into place; you can override this variable
+	# to specify a built-in configuration to use other than conf/mig-loader-conf.go.inc
+	cp $(LOADERCONF) mig-loader/configuration.go
 	$(GO) build $(GOOPTS) -o $(BINDIR)/mig-loader $(GOLDFLAGS) mig.ninja/mig/mig-loader
 	if [ $(OS) = "darwin" -a ! -z "$(OSXPROCSIGID)" ]; then \
 		codesign -s "$(OSXPROCSIGID)" $(BINDIR)/mig-loader; \