Multiple NIC support

This patch adds to support multiple NIC initialization on loader.cc.

Signed-off-by: Takuya ASADA <syuu@dokukino.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
run.py: Do not run Xen guests with user mode networking implicitely

Xen guests do not support user mode networking.
Fall back to qemu when hypervisor detection used and no external
networking configured.

This logic is required for build to support Xen hosts properly.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
loader.py: make 'osv info threads' display the thread on which joiner waits

Saves a bit of manual work.

Example:

  gdb$ osv info threads
  0 (0x1de9e08) cpu0x0 waiting    sched::thread::join() at core/sched.cc (SNIP)
	joining on 0xffffc0003e41e010

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Skip lo0 when initializing interfaces in loader.cc

Attempt to reassign IP for lo0 fails and leaves it without an address.

This breaks tomcat:

  SEVERE: StandardServer.await: create[localhost:8005]:
  java.net.BindException: Address not available

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>