Updating HDFS to use CHPL_AUXIO_INCLUDE and CHPL_AUXIO_LIBS

Changing HDFS to use CHPL_AUXIO_INCLUDE and CHPL_AUXIO_LIBS for library and include paths. Updating README.hdfs to reflect this as well.
I think this could be a little cleaner using the "?=" operator (sets only if the variable is not already set):

```
CHPL_AUXIO_INCLUDE ?= \
	-I$(JAVA_INSTALL)/include \
	-I$(JAVA_INSTALL)/include/linux \
	-I$(HADOOP_INSTALL)/src/c++/libhdfs
CHPL_AUXIO_LIBS ?= \
	-L$(JAVA_INSTALL)/jre/lib/amd64/server \
	-L$(HADOOP_INSTALL)/c++/Linux-amd64-64/lib

GEN_LFLAGS += \
	$(CHPL_AUXIO_INCLUDE) \
	$(CHPL_AUXIO_LIBS)
```