imagebuilder: companion fix for redundant abi-versioned packages hack

The find command fails if the same files are overwrite by itself:
...
find /workdir/bin/targets/malta/le/packages /workdir/bin/packages/mipsel_24kc/base /workdir/bin/packages/mipsel_24kc/luci /workdir/bin/packages/mipsel_24kc/packages /workdir/bin/packages/mipsel_24kc/routing /workdir/bin/packages/mipsel_24kc/telephony /workdir/bin/packages/mipsel_24kc/video -type f -name '*.apk' \
        -exec cp -fpR -t /workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/ {} +
cp: will not overwrite just-created '/workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/libext2fs2-1.47.3-r1.apk' with '/workdir/bin/packages/mipsel_24kc/base/libext2fs2-1.47.3-r1.apk'
cp: will not overwrite just-created '/workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/libcomerr0-1.47.3-r1.apk' with '/workdir/bin/packages/mipsel_24kc/base/libcomerr0-1.47.3-r1.apk'
cp: will not overwrite just-created '/workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/libe2p2-1.47.3-r1.apk' with '/workdir/bin/packages/mipsel_24kc/base/libe2p2-1.47.3-r1.apk'
cp: will not overwrite just-created '/workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/libjson-c5-0.18-r1.apk' with '/workdir/bin/packages/mipsel_24kc/base/libjson-c5-0.18-r1.apk'
...

Since the "find + exex $(CP)" is intented to execute cp with -f flag for
overwrites, it should success in that case or at least not fail.
Change to a equivalent "rsync" command which does it correctly.

This is needed for the new "shared" abi-versioned packages which are
going to appear in two directories after the other commit included in
this PR/series is applied.

After:
        rsync -a --include='*.apk' --exclude='*' \
        /workdir/bin/targets/malta/le/packages/ /workdir/bin/packages/mipsel_24kc/base/ /workdir/bin/packages/mipsel_24kc/luci/ /workdir/bin/packages/mipsel_24kc/packages/ /workdir/bin/packages/mipsel_24kc/routing/ /workdir/bin/packages/mipsel_24kc/telephony/ /workdir/bin/packages/mipsel_24kc/video/ \
        /workdir/build_dir/target-mipsel_24kc_musl/openwrt-imagebuilder-malta-le.Linux-x86_64/packages/

Signed-off-by: Mario Andrés Pérez <mapb_@outlook.com>

Author: map-b

target/imagebuilder/Makefile

@@ -76,8 +76,9 @@ ifeq ($(CONFIG_IB_STANDALONE),)
 		-name 'kernel$(PACKAGE_VERSION_SEPARATOR)*.$(PACKAGE_SUFFIX)' \) \
 	  -exec $(CP) -t $(PKG_BUILD_DIR)/packages {} +
 else
-	$(FIND) $(wildcard $(PACKAGE_SUBDIRS)) -type f -name '*.$(PACKAGE_SUFFIX)' \
-		-exec $(CP) -t $(PKG_BUILD_DIR)/packages/ {} +
+	rsync -a --include='*.$(PACKAGE_SUFFIX)' --exclude='*' \
+	$(foreach dir,$(wildcard $(PACKAGE_SUBDIRS)),$(dir)/) \
+	$(PKG_BUILD_DIR)/packages/
 endif
 
 ifneq ($(CONFIG_SIGNATURE_CHECK),)