add the argument WORKDIR in daisy-img-modify.sh

add the argument WORKDIR in daisy-img-modify.sh

the daisy install tmp workdir can be configurated as an input
argument in deploy.sh,and it also should be used in subshell
daisy-img-modify.sh,so add the input argument -w workdir
in daisy-img-modify.sh.

1.add an input argument -w workdir in daisy-img-modify.sh.
2.modify the WORKDIR default value to /tmp/workdir/daisy.
3.code refactor to put the centos7.qcow2 file clean statement
from the deploy.sh to daisy-img-modify.sh.

Change-Id: Id375a15ad2839c209329e644c5e032d044604e7d
Signed-off-by: zhongjun <zhong.jun@zte.com.cn>