Use nodetool to get VM PID

Rather than use `ps`, `grep` and `awk` to get the `beam.smp` process id,
use the `os:getpid` function.

Also, provide a `pid` command to facilitate retrieving the VM's process
id at a later time. Useful for when running via `monit`, for instance.
Add `pid` to usage
only unique lib dirs should be used to save time/confusion
Merge pull request #284 from lukebakken/features/lrb/get-node-pid

Use nodetool to get VM PID
Explicitly use 'exit 1' to exit

Fixes #286

Using `exit $?` will exit with 0 status even in error conditions. I
believe this is due to the fact that the `if` statement sets `$?`
somehow. This could be a bug in the version of `bash` I'm using (as
`/bin/sh`):

```
$ /bin/sh --version
GNU bash, version 4.3.30(1)-release (x86_64-unknown-linux-gnu)
```
No need to output -1 since error codes are straightened out.
Merge pull request #287 from lukebakken/issues/lrb/286

Explicitly use 'exit 1' to exit
Merge pull request #285 from tsloughter/master

only unique lib dirs should be used to save time/confusion