resulttool: Add support to create test report in JUnit XML format

resulttool: Add support to create test report in JUnit XML format

This adds the functionality to convert the results of the
testresults.json file to a unit test report in JUnit XML format. The
unit test report can be used in the CI/CD pipeline to display the test
results.

To use the resulttool scripts, first source oe environment, then run the
entry point script to look for help.
	$ resulttool

To generate the unit test report, execute the below
	$ resulttool junit <json_file>

By default the unit test report is stored as
<build_dir>/tmp/log/oeqa/junit.xml.

Signed-off-by: Clara Kowalsky <clara.kowalsky@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>