Cherry-pick 7.10 changes to 7.11.

Cherry-picked commits:
    e24220ea gdb: disable python when python is not available.
    d73c5467 use snprintf instead of strlcpy for portablitly
    c64829b2 Fallback to open if multifs_open fails.
    21770732 Fix gdbserver process interruption.
    b711aa82 Add Unix domain socket support to gdbserver 7.9.1

Change-Id: I2cba7ae5c05503afb81f732cbd78440ebd2c45e8