On creating actor instances in Mesos

[Alex Rukletsov]

Folks,

I've noticed recently that some actors do not specify a distinguishable
actor ID. As a result, it may be hard to match output to a specific actor,
for example an excerpt from "__processes__" endpoint:

[{"events":[],"id":"(10)"},{"events":[],"id":"(11)"},{"events":[],"id":"(1279859)"},{"events":[],"id":"(15)"},
... ]

Every time you create an actor, i.e., a `ProcessBase` instance, you most
probably want to give it a meaningful id. Consider `StatusUpdateManager`.
Currently, the code does not specify the ID:

StatusUpdateManagerProcess::StatusUpdateManagerProcess(const Flags& _flags)
  : flags(_flags), paused(false) {}

Instead, a preferred way of calling the `StatusUpdateManagerProcess` c-tor
would be:

StatusUpdateManagerProcess::StatusUpdateManagerProcess(const Flags& _flags)
  : ProcessBase(process::ID::generate("status-update-manager")),
    flags(_flags),
    paused(false) {}

Best,
Alex