qemu.test Add check_rom test 

This case check that roms are loaded once not twice.
changes from v1:
  1) Modified check function to set().

changes from v2:
  1) Add some comments.
  2) Delete the qmp_cmd parameter.

changes from v3:
  1) update some error contexts
  2) remove the for loop

changes from v4:
  1) make re string configure.
  2) update the Fail message

changes from v5:
  1) add check available for fw_filter and addr_filter parameter

Signed-off-by: Shuping Cui <scui@redhat.com>