Create variant specific output folders

[sergeys-opera]

LicenseReportTask needs to run per variant (as variant dependencies might differ), thus, there might be multiple LicenseReportTask tasks defined in the project, e.g. licenseDebugReport or licenseReleaseReport. But all such tasks mark the same folder as their output making it impossible to add new tasks that depend on them. Gradle would think, for example, that a custom task processLicenseDebugReport is dependent on both licenseDebugReport and licenseReleaseReport as it uses files from the output folder of those tasks, while in reality it only depends on licenseDebugReport:

Reason: Task 'processLicenseDebugReport' uses this output of task
  'licenseReleaseReport' without declaring an explicit or implicit dependency
  This can lead to incorrect results being produced, depending on what order the
  tasks are executed.

There are two ways to fix this I think:

1. Declare each output file of LicenseReportTask as @Output
2. Create different output folders per build variant, e.g. licencesDebug and licensesRelease

[realdadfish]

Kind of a duplicate of #226

[jaredsburrows]

Closed on duplicate.