Cleanup: PeerConnector session initialization method

Cleanup: PeerConnector session initialization method

* rename initializeSsl() method to initializeTls()

* use SessionPointer instead of SessionPtr

* return value is best used in boolean expressions, so make it bool
  this also resolves some template issues with SessionPointer return type.

* rename the session parameter to serverSession which better documents what
  it is than 'ssl', and distinguishes it from clientSession in child methods
  which have to deal with both.