utils_params.object: Avoid quotation marks for object paramters.

For parameter like "vms", if we pass value in this format:
vms = "vm1 vm2 vm3",
vms will be recognised as '"vm1', 'vm2' and 'vm3"'.
So strip it when analysing.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>