base-files: don't ship local build key when on buildbot

Including the local build key in /etc/opkg/keys isn't feasible when
building on the buildbot: The included key collides with its copy
already in openwrt-keyring which breaks the ImageBuilder.
Not including a locally generated key also makes the base-files package
more reproducible.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/base-files/Makefile

@@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/version.mk
 include $(INCLUDE_DIR)/feeds.mk
 
 PKG_NAME:=base-files
-PKG_RELEASE:=217
+PKG_RELEASE:=218
 PKG_FLAGS:=nonshared
 
 PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ $(GENERIC_PLATFORM_DIR)/base-files/
@@ -118,12 +118,14 @@ ifdef CONFIG_SIGNED_PACKAGES
 
   endef
 
+ifndef CONFIG_BUILDBOT
   define Package/base-files/install-key
 	mkdir -p $(1)/etc/opkg/keys
 	$(CP) $(BUILD_KEY).pub $(1)/etc/opkg/keys/`$(STAGING_DIR_HOST)/bin/usign -F -p $(BUILD_KEY).pub`
 
   endef
 endif
+endif
 
 ifeq ($(CONFIG_NAND_SUPPORT),)
   define Package/base-files/nand-support