Bugfix validate default parameters

First commit fixes the reserved parameters overwriting the params set by the user.  If user creates a `pollInterval` parameter we validate that its above and below the min and max and use that value if it is available, otherwise use the defaults.

Second commit fixes a bug where you disable a plugin, then re-enable it.  Currently the pluginInfo overwrites the new cfg and the plugin fails to start:

Before:
```
graphdat-relay running (using node v0.8.26)
Remote configuration enabled
New config found, modified Mon Dec 23 2013 17:01:29 GMT-0800 (PST)
Plugin diskuse-test validated
Loaded plugin diskuse-test
New config found, modified Mon Dec 23 2013 17:02:10 GMT-0800 (PST)
Stopping plugin diskuse-test because it is disabled
Skipping plugin diskuse-test, because it is disabled
New config found, modified Mon Dec 23 2013 17:02:13 GMT-0800 (PST)
Skipping plugin diskuse-test, because it is disabled
```

After
```
graphdat-relay running (using node v0.8.26)
Remote configuration enabled
New config found, modified Mon Dec 23 2013 16:52:02 GMT-0800 (PST)
Plugin diskuse-test validated
Loaded plugin diskuse-test
New config found, modified Mon Dec 23 2013 16:59:47 GMT-0800 (PST)
Stopping plugin diskuse-test because it is disabled
Skipping plugin diskuse-test, because it is disabled
New config found, modified Mon Dec 23 2013 17:00:26 GMT-0800 (PST)
Plugin diskuse-test validated
diskuse-test: Config changed, restarting
Loaded plugin diskuse-test
diskuse-test: Writing param.json
```