Make the platform process connect path less chatty.

Summary:
If a stream contains an empty string, no need to append it to the output
(otherwise we end up with a blank line). Also, no need to print a status
message when the state changes to connected, as this string brings no
information -- "Process 0" does not mean anything to the user, and the
process being connected has no meaning either.

Test Plan:
Connect to a remote linux platform mode daemon with `platform select
remote-linux` followed by `platform connect ...`, create a target and
run it, observe the output. Also, run the full test suite (dosep.py).

Before:
    (lldb) [...] connect, etc.
    (lldb) r
    Process 0 connected

    Process 5635 launched: '/Users/sas/Source/test' (x86_64)
    Process 5635 stopped

After:
    (lldb) [...] connect, etc.
    (lldb) r
    Process 5635 launched: '/Users/sas/Source/test' (x86_64)
    Process 5635 stopped

Reviewers: tfiala, vharron, clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D6593