Cleanup helper.h classes

[yadij]

Polish up the classes in helper.h to use proper constructors as the
caller API for creation + initialization. Use C++11 initialization for
default values.

• no "virtual" in helper class destructor declaration could create
  memory leaks in future (poorly) refactored code; the gained protection
  is probably worth adding the (currently unused) virtual table to the
  helper class; resolves Coverity issue CID 1461141 (VIRTUAL_DTOR)
• missing Comm::Connection timers initialization on helper startup
• multiple initialization of values used for state accounting
• initialization of booleans to non-0 integer values
• initialization of char using numeric values
• missing mgr:filedescriptors description for helper sockets

[yadij]

This is a repeat of PR #719 with fixes by Christos, and additional debugging outputs by myself to review the helper I/O traffic.

I think we have the problems ironed out properly. But would still like some third-party testing to confirm no more weirdness happens before clearing for merge.

[rousskov]

Amos would still like some third-party testing to confirm no more weirdness happens before clearing for merge.

rousskov added S-waiting-for-more-reviewers and removed S-waiting-for-QA labels

S-waiting-for-QA is for PRs that need QA team attention -- that team needs to add or fix something before the PR can be merged. The current automated tests do not cover helpers, and I doubt Amos would want this PR to wait until they do.

We do not have a GitHub label that covers "3rd party testing" waiting well, so I used S-waiting-for-more-reviewers. We can add S-waiting-3rd-party and use it here instead.