kvm tools: Print out important command line options at startup

It's important to know what the guest configuration looks like when debugging
issues so print out important command line options at startup:

  $ ./kvm run -k ../../arch/x86/boot/bzImage -m 512
    # kvm run -k ../../arch/x86/boot/bzImage -m 512 -c 1

Suggested-by: Ingo Molnar <mingo@elte.hu>
Cc: Asias He <asias.hejun@gmail.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>