Fix broken test in vagrant boostrap script

The file path was not properly passed to the '-x' test which caused it
to always return true.

This commit simplifies the test for existing command by relying only on
the exit code of `type` rather than checking that the file path is
executable.

Change-Id: Iaf47d92ff9fd1ef34d8d7492c08ec24d2b8a9536
Closes-Bug: #1635341