html report generation broken

[jspong]

In adding python 3 support, ducktape/templates/report/report.html was updated use {{ }} for variable interpolation instead of %s.

React fails to render the html report with the following error:

Uncaught Error: Parse Error: Line 162: Unexpected token {
    at http://confluent-platform-branch-builder-system-test-results.s3-us-west-2.amazonaws.com/2020-03-25--002.1585183175--jspong--HEAD--04b96f8/report.html

"tests": {{num_tests}},
         ^
    at throwError (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5119:21)
    at throwUnexpected (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5181:9)
    at parseObjectProperty (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5621:17)
    at parseObjectInitialiser (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5697:28)
    at parsePrimaryExpression (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5864:20)
    at parseLeftHandSideExpressionAllowCall (https://unpkg.com/[email protected]/dist/JSXTransformer.js:5967:61)
    at parsePostfixExpression (https://unpkg.com/[email protected]/dist/JSXTransformer.js:6007:20)
    at parseUnaryExpression (https://unpkg.com/[email protected]/dist/JSXTransformer.js:6074:16)
    at parseBinaryExpression (https://unpkg.com/[email protected]/dist/JSXTransformer.js:6164:16)
    at parseConditionalExpression (https://unpkg.com/[email protected]/dist/JSXTransformer.js:6224:16)

We can pretty easily update ducktape/tests/reporter.py to treat this as a Jinja2 template and interpolate the values properly.