slave.mk: add SONIC_PLATFORM_API_PY2 as dependency of host
sonic_debian_extension.j2: install sonic_daemon_base and Mellanox-specific sonic_platform on host
mlnx-platform-api.mk: export mlnx_platform_api_py2_wheel_path for sonic_debian_extension.j2
sonic-daemon-base.mk: export daemon_base_py2_wheel_path for sonic_debian_extension.j2
daemon_base.py: hind unnecessary dependency of swss_common on host
DaemonBase is to wrap the common function of daemons, such as logging,
signal handling, db connector, load specific platform plugins.
Signed-off-by: Kevin Wang <kevinw@mellanox.com>