Remove pid from master pidfile name. Closes #20.

[strk]

There's no use of a .pid file storing the PID if you need to know
the PID in order to read the file...

[strk]

NOTE: the TravisCI failure is due to unstable test results, independently from the patch.
Simply applying this patch fixes the test here:

diff --git a/test/cluster-test.js b/test/cluster-test.js
index 3ebe6e5..282f3ab 100644
--- a/test/cluster-test.js
+++ b/test/cluster-test.js
@@ -354,7 +354,7 @@ module.exports = {
                 var re = new RegExp('status=AVAILABLE&ServeTraffic=true&ip=(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)&hostname=' + hostname + '&port=3000&time=.*');
                 var result = re.exec(body);
                 test.ok(result !== null,
-                    'expected:status=AVAILABLE&ServeTraffic=true&ip=<Network IP>&hostname=' + hostname + '&port=3000&time=.*');
+                    'expected:status=AVAILABLE&ServeTraffic=true&ip=<Network IP>&hostname=' + hostname + '&port=3000&time=.*' +"");

                 request({uri: 'http://localhost:3000/ecv/disable', method: 'POST'}, function (error, response, body) {
                     // Wait for signal to propagate to workers

The patch is only appending an empty string to the failure message !

[strk]

Tried a rebase with #31 -- does pass npm test for me