(#3757) Implement json-based lockfiles

This commit does the following:

1. Refactors our main lockfile class to accept a data object as an argument to the #lock method. This data can then be retrieved at any time while the lock is held; the implementation is to write the hash as JSON to the lockfile. This will allow external tools to read it without calling into puppet code.
2. Refactor pidlock to use the above--but only serializing a String (the pid) to the file.
3. Refactor disabler to use the above, with a Hash containing a key/value pair identifying the "disabled" message.
4. Fix and clean up spec tests.