[ASTImporter] Changed use of Import to Import_New in ASTImporter.

Reviewers: a.sidorin, shafik, a_sidorin

Reviewed By: a_sidorin

Subscribers: gamesh411, a_sidorin, dkrupp, martong, Szelethus, cfe-commits

Differential Revision: https://reviews.llvm.org/D53818

llvm-svn: 347752