Code coverage

[AnonymousWalker]

As sonarqube only reads and analyzes from code coverage report file (.xml is best option), we need the jacoco java plugin to generate coverage report at project level.
To aggregate the reports from subprojects, a custom JacocoReport task at root gradle file is needed to iterates through the project tree and collect the .exec file generated from jacoco plugin.

Also, this report task should execute after running all the tests.

Helpful resources:
Github issue 8881
Gradle documentation

This change is 

[mXaln]

Reviewed 1 of 2 files at r1, 1 of 3 files at r3, 3 of 3 files at r4, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @AnonymousWalker and @jsarabia)

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build.gradle line 30 at r4 (raw file):

jacoco {
    toolVersion = "0.8.7" // use this jacoco version to avoid error

Please move the version number to dependencies.gradle file

[AnonymousWalker]

Reviewable status: 4 of 6 files reviewed, 1 unresolved discussion (waiting on @jsarabia and @mXaln)

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build.gradle line 30 at r4 (raw file):

Previously, mXaln (Maxim) wrote…

Please move the version number to dependencies.gradle file

Thanks for reminding!

[jsarabia]

Reviewable status: 4 of 6 files reviewed, 1 unresolved discussion (waiting on @mXaln)

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build.gradle line 30 at r4 (raw file):

Previously, AnonymousWalker (Tony) wrote…

Thanks for reminding!

could this be placed under the allprojects block, instead of here and in the subprojects block?