gdb: preserve `|` in connection details string

gdb: preserve `|` in connection details string

Consider this GDB session:

  $ gdb -q
  (gdb) target remote  | gdbserver - ~/tmp/hello.x
  Remote debugging using | gdbserver - ~/tmp/hello.x
  ... snip ...
  (gdb) info connections
    Num  What                              Description
  * 1    remote gdbserver - ~/tmp/hello.x  Remote target using gdb-specific protocol
  (gdb) python conn = gdb.selected_inferior().connection
  (gdb) python print(conn.details)
  gdbserver - ~/tmp/hello.x
  (gdb)

I think there are two things wrong here, first in the "What" column of
the 'info connections' output, I think the text should be:

  remote | gdbserver - ~/tmp/hello.x

to correctly show the user how the connection was established.  And in
a similar fashion, I think that the `details` string of the
gdb.TargetConnection object should be:

  | gdbserver - ~/tmp/hello.x

This commit makes this change.  Currently the '|' is detected and
removed in gdb/serial.c.  The string passed to the pipe_ops
structure (from gdb/ser-pipe.c), doesn't then, contain the `|`, this
is instead implied by the fact that it is a pipes based implementation
of the serial_ops interface.

After this commit we still detect the `|` in gdb/serial.c, but we now
store the full string (including the `|`) in the serial::name member
variable.

For pipe based serial connections, this name is only used for
displaying the two fields I mention above, and in pipe_open (from
gdb/ser-pipe.c), and in pipe_open, we now know to skip over the `|`.

The benefit I see from this change is that GDB's output now more
accurately reflects the commands used to start a target, thus making
it easier for a user to understand what is going on.