Improve GCov plugin: overall coverage validation

[IvanRibakov]

Is this User Story based on a PBI?

https://indigital.atlassian.net/browse/INESRP-113

Description

As a:

develop

I need to:

get automated feedback if overall project coverage is below a set threshold

So that:

I can ensure that project always has sufficient code coverage

Assumptions

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

Acceptance Criteria

1. New configuration item in project.yml under :gcov: that allows to set minimum acceptable code coverage threshold
2. If, after running ceedling gcov:x, overall code coverage is below new threshold, command should terminate with an error code
3. ...

Sub-tasks:

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