copy vhd into the testing location when source vhd location is different

[LiliDeng]

just a draft, 3 things need to be fixed.

• when reuse rg, this logic still be executed, need fix.
• need shorten the copied vhd, currently it is too long.
• also if the vhd has been copied, if the sas url is different, it will still be copied again.

[squirrelsc]

Can you provide the reason of this change in the commit description?

[squirrelsc]

• also if the vhd has been copied, if the sas url is different, it will still be copied again. Is it expected behavior, or something you need to fix?

[LiliDeng]

@squirrelsc during my testing, I found if set concurrency as 2, then there are 2 sas url generated, vhd will be copied twice, can this design be accepted?