build.py: Really run in GDB when using --debug.

The usage (--help) says: "Build with debug support; run in GDB", but
GDB was only used when using the D-Bus daemon.  Run a libwrap built
Jami with GDB as well.

* build.py (run_run): Disable SIGINT when using GDB, and invoke the
Jami client with GDB.  Disable output redirection to logs when using GDB.

Change-Id: Icf3415a3d1fbb87f193d0ede07cb1e1fbb179ce2