Fix race condition crash on startup

[steven-sheehy]

Fixes #74

• Adds a keepalived.IsRunning() method that checks if keepalived.Start() has been called and that the main keepalived pid file exists.
• Waits for keepalived to be running before reloading configuration. This ensures keepalived's SIGHUP handler is running before sending a SIGHUP.
• Enhances the health check to also check if main and vrrp processes are running.

[steven-sheehy]

/assign @aledbf

[coveralls]

Coverage decreased (-0.3%) to 15.097% when pulling e9ffc21 on steven-sheehy:keepalived-crash-startup into 34a46af on aledbf:master.

[aledbf]

@steven-sheehy thanks!

[steven-sheehy]

Any chance of a release soon?

[aledbf]

@steven-sheehy done