logger: move writer/sock fd to fd_entity struct

logger: move writer/sock fd to fd_entity struct

writers and sockets fds are registered in epoll loop
their fds are placed in the common fd_entity struct.
adding/removing fds to logger's epoll are redesigned
to reflect this pattern

free logger extra readers possible memory leak bugfix
and style minor changes

Change-Id: Iccb7ac50658494451290fa98ad170247a141099e