[WIP] odoo-tester: use diff-cover to measure changed code coverage

[davidmcgaw]

Changes I made to docker files:

• install the diff-cover package

• The sub-folders from udes-open are copied to the docker image. However this excludes the .git folder, which is used by diff-cover to determine code changes - solution: copy the parent folder.

• diff-cover needs coverage data to be collected when the test is run relative to the "root" folder (that contains the .git folder):

• All the coverage & diff-cover commands needs to be run from the "root" directory - solution: change to the "root" folder before running

• The coverage commands create files in the "root" directory which require write permissions - solution: update permissions on the root folder to allow coverage data to be written

This is connected to another PR (in udes-open: github.com/unipartdigital/udes-open/pull/229) with the change:

• Copy the parent folder changes the location of modules. There is some code to identify modules which are now wrong - solution: update the code to look for modules.

Below is an example of the results of calling "diff-cover coverage.xml":

-------------
Diff Coverage
Diff: origin/master...HEAD, staged and unstaged changes
-------------
addons/service_job/models/sale_order.py (0.0%): Missing lines 26,31
addons/service_job/models/servicejob.py (66.7%): Missing lines 982
-------------
Total:   5 lines
Missing: 3 lines
Coverage: 40%
-------------

Each file with changes in the diff is listed along with:

• the percentage of the changed lines of code that are executed tests
• a list of the lines of code that are not hit (if the percentage is <100%)

Also there is a summary of changed lines and the number of lines that are executed across all the files in the diff.

[mcb30]

Please match the existing commit message format