Parallels provider: Fixed mount options for synced folders

Mount options "dmode" and "fmode" are unavailable for "prl_fs"
filesystem. Use mount option "share", which provides liberal access
permissions to shared folders.

Related issue:
https://github.com/Parallels/vagrant-parallels/issues/135
Merge pull request #1090 from legal90/master

Parallels provider: Fixed mount options for synced folders