Allow explicit use of ccache during compilations.
- If $CCACHE is set it will be used to prefix calls to gcc. Enable ccache by compiling with CCACHE=ccache
- If $CCACHE is set and being used it will be displayed in the CINFO block.
Merge into master from pull request #3:
Allow explicit use of ccache during compilations. (https://github.com/floodlight/infra/pull/3)