rcmgr: *: Always close connscope

[MarcoPolo]

Fixes #2033.

Closes #2025 and closes #2031 .

The general pattern here is replacing

func ...Dial() {
  connScope := ...
  
  err := ...
  if err != nil {
    connScope.Done()
  }
  
    err := ...
  if err != nil {
    connScope.Done()
  }
  
    err := ...
  if err != nil {
    connScope.Done()
  }
}

With:

func ...Dial() {
  connScope := ...
  
  c, err := dialWithScope
  
  if err != nil {
    connScope.Done()
    return nil, err
  }
  
  return c, nil
}

func dialWithScope(..., connScope) {
  if err != nil {
     return nil, err
  }
}

[marten-seemann]

Good idea to fix this class of issues once and for all!