Collect code coverage in screenshotter tests (#1644)

* Collect code coverage in screenshotter tests

* Using instanbul, no additional dependencies required as they are part 
of jest
* Collect in CircleCI builds and upload to Codecov

* Remove clover report

package.json

@@ -21,6 +21,7 @@
     "babel-eslint": "^8.1.2",
     "babel-jest": "^23.0.1",
     "babel-loader": "^7.1.4",
+    "babel-plugin-istanbul": "^4.1.6",
     "babel-plugin-transform-class-properties": "^6.23.0",
     "babel-plugin-transform-runtime": "^6.15.0",
     "babel-plugin-version-inline": "^1.0.0",
@@ -40,6 +41,8 @@
     "fs-extra": "^7.0.0",
     "greenkeeper-lockfile": "^1.15.1",
     "husky": "^1.0.0-rc.8",
+    "istanbul-api": "^1.3.1",
+    "istanbul-lib-coverage": "^1.2.0",
     "jest": "^23.0.1",
     "jest-serializer-html": "^5.0.0",
     "js-yaml": "^3.10.0",