Allow easy customization of binlog name

Currently the build scripts seem to have just a boolean for whether or not a binlog is produced. For restore, the binlog is named `ToolsetRestore.binlog`, and for build it's `Build.binlog`. It would be a nice idea to allow customization.

Scenario for testfx: we have a build step and a test step. We would like to see both binlogs.

https://github.com/microsoft/testfx/blob/e5345132464e5b6ab26cd6fc2c6f8f44854d548e/azure-pipelines.yml#L88-L104