Feature/dingpf individual unittest log

[dingp]

This PR changes dbt-build.py, so that:

• Unit test and linting log files are organized into sub-directories;
• A summary of unit test results is created at the end of all unit tests.

[jcfreeman2]

Ran some unit testing and linting and the saved results look good

[jcfreeman2]

One quick thing: it may be worth considering consistency between the filenames for individual unit tests vs. the summary. E.g., right now in a given subdirectory we have:

dfmodules_DataFlowOrchestrator_test_unittest_Fri_Mar_11_17_18_24_CST_2022.log
unit_test_summary.log

so it's worth considering whether both, or neither, of the filenames should bear the timestamp.

[dingp]

the timestamp is already in the directory name, so I consider removing it from the name of individual test logs.

[dingp]

similarly for the linting log, the datestring is included in the dir name, so removing it from the log file's name.