Minor fixes for project importer

[lihaoyi]

• If no test framework can be identified, default to TestModule.Junit4 to allow the build to at least compile
• Add a space between the lazy val $lhs and the following : to avoid parsing errors when lhs ends with a _

Noticed these while trying to get MIMA imports working

[lihaoyi]

Looks like the failure in example.migrating.javalib[3-maven-complete-large].packaged.daemon's page-object test suite is that it is incorrectly configured in Maven: it does not a test framework or test dependencies configured, and thus doesn't run when you use ./mvnw clean test -pl page-object -am.