CI: update ARM 32 bit build to Zesty

Also, use more official / better maintained Docker image repo.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

scripts/build/Dockerfile.armv7hf.hdr

-FROM armv7/armhf-ubuntu
+FROM arm32v7/ubuntu:zesty
 
 COPY scripts/build/qemu-user-static/usr/bin/qemu-arm-static /usr/bin/qemu-arm-static

scripts/build/Makefile

@@ -37,11 +37,9 @@ $(1)-clang: $(1)
 endef
 $(foreach t,$(TARGETS),$(eval $(call CLANG_DEP,$(t))))
 
-%-clang:	DB_CC=--build-arg CC=clang-3.8
+%-clang:	DB_CC=--build-arg CC=clang
 %-clang:	DB_ENV=--build-arg ENV1=CCACHE_CPP2
-alpine-clang:	DB_CC=--build-arg CC=clang
-aarch64-clang:	DB_CC=--build-arg CC=clang
-ppc64le-clang:	DB_CC=--build-arg CC=clang
+s390x-clang:	DB_CC=--build-arg CC=clang-3.8
 .PHONY: $(TARGETS_CLANG)
 
 clean: