action/import: Regen SourceVmUuid by nokogiri

Instead of using '--regenerate-src-uuid' while box register, we are doing the same manually,
by editing 'config.pvs' via nokogiri XML library.
config: Renamed option 'regen_box_uuid' to 'regen_src_uuid'
Fixed unit tests
Merge pull request #159 from Parallels/f-regen_src_uuid

Fixed regenerate SourceVmUuid