Removed deprecated testReportDir property.

Since the Android Gradle plugin 0.9.x enforces Gradle >= 1.10 we
can remove the deprecated `testReportDir` and use the new
`reports.html.destination` property.

Closes #15.
Changes Plugin to search for plugins that are instances of
App/Library Plugins.

Closes #12.
Update plugin to work with android plugin version 0.10.x.