remove the log.error.... of the catch section of executeTask(... method.
Log should be performed by the method catching the throwed exception. Else we will log twice the exception.

FROM:
installContext.error("Unable to execute PostMigrationTask for the following module:"+getModuleName(), e);
log.error("Unable to execute PostMigrationTask for the following module:"+getModuleName(), e);
reportException(e);
throw new TaskExecutionException(e.getMessage());

TO:
installContext.error("Unable to execute PostMigrationTask for the following module:"+getModuleName(), e);
reportException(e);
throw new TaskExecutionException("Unable to handle PostMigrationTask for the following module:"+getModuleName(),e);