fs_config: modularize fs_config_generator

This internally structures fs_config_generator.py to be able
to plug in generators to produce different outputs. This
prepares this tool for group and pwd file outputs.

Test: Checked diff and hash of before and after files.
Change-Id: Ie558518ac227dd946d70ab48027698b72a9bc94a
Signed-off-by: William Roberts <william.c.roberts@intel.com>
diff --git a/tools/fs_config/Android.mk b/tools/fs_config/Android.mk
index fb4a0c4..7d4d271 100644
--- a/tools/fs_config/Android.mk
+++ b/tools/fs_config/Android.mk
@@ -84,7 +84,7 @@
 gen := $(local-generated-sources-dir)/$(ANDROID_FS_CONFIG_H)
 $(gen): PRIVATE_LOCAL_PATH := $(LOCAL_PATH)
 $(gen): PRIVATE_TARGET_FS_CONFIG_GEN := $(TARGET_FS_CONFIG_GEN)
-$(gen): PRIVATE_CUSTOM_TOOL = $(PRIVATE_LOCAL_PATH)/fs_config_generator.py $(PRIVATE_TARGET_FS_CONFIG_GEN) > $@
+$(gen): PRIVATE_CUSTOM_TOOL = $(PRIVATE_LOCAL_PATH)/fs_config_generator.py fsconfig $(PRIVATE_TARGET_FS_CONFIG_GEN) > $@
 $(gen): $(TARGET_FS_CONFIG_GEN) $(LOCAL_PATH)/fs_config_generator.py
 	$(transform-generated-source)