driver: Use '--no-header' option to exclude 'INFO' from prlctl output.

Some read_* methods became universal for PD 8,9,10. We don't need to override them anymore.
driver: added 'read_vm_option' method
driver refactoring
Fixed unit tests
driver: Handle errors during 'register' and 'unregister'
action/import: Refactoring
action/import: Use template name detected by parsing 'config.pvs'
action/export: Refactoring
'prl_fs' mount on linux: added sanity check for mount options [GH-135]
Provider is parallel now

Multiple actions may be run in parallel.
Fixed Travis builds

Removed unused bsdtar
Set bundler version