Improve GCov plugin: configuration option to fail test run if uncovered files are detected

[IvanRibakov]

Is this User Story based on a PBI?

https://indigital.atlassian.net/browse/INESRP-114

Description

As a:

developer

I need to:

be able to configure GCov plugin in a way that it doesn't allow presence of uncovered source files

So that:

reported code coverage figure is accurate (takes into account all project source files, not just those that are currently covered)

Assumptions

1. ...
2. ...
3. ...

Acceptance Criteria

1. New configuration item in project.yml under :gcov: that allows to enable/disable strict checking of uncovered source files
2. If, after running ceedling gcov:x, uncovered source files are detected, command should terminate with an error code
3. ...

Sub-tasks:

1. 1 - ...
2. 2 - ...
3. 3 - ...