Add missing coverage deps

Testing Done:
CI is green at https://travis-ci.org/pantsbuild/pants/builds/37057783

Reviewed at https://rbcommons.com/s/twitter/r/1117/
Memoize Address.__hash__ computation.

I noticed during profiling that it is a major hotspot and a very easy
change.  This is unsurprising: addresses are dictionary keys for many of
the fundamental structures in pants.

Also hoist spec_path and target_name into private attributes exposed by properties.

Testing Done:
Travis is being flakey.  ci.sh passed and a previous run of travis was green.

Reviewed at https://rbcommons.com/s/twitter/r/1118/
Read values for a handful of options in the new way.

Provides an example for mass migration.

Also fixes an issue where we weren't "descoping" old-style options
in all the places they could appear.

Reviewed in https://rbcommons.com/s/twitter/r/1114/