Factor test building and test running

[brettviren]

Currently there is not a good separation between building and running of tests.

Desired end state: always build test_* and doctests. Only run when ./wcb --tests given.

[brettviren]

The auto close of that commit didn't fire due to spelling but in any case I want to keep this open as the current build policy is not satisfying.

Here are features that are true now that should be kept:

• From a green field a ./wcb builds everything including atomic tests but runs no tests.
• A ./wcb --tests is needed to run the atomic tests.

Here are new features that are wanted:

• Touching a file, eg in util/ but doing a ./wcb --target=wcdoctest-util ONLY builds the targets (eg, libWireCellUtil and the actual executable) that are needed for that --target. Right now, this will build all things that depend on the touched file.

[brettviren]

It would be nice to have a "development" and "release" build mode. In "dev" mode, run any doctest that got rebuilt. In "rel" mode, do not build nor run any tests.

[brettviren]

This issue has been extended beyond what that auto-close commit provides.