updated backend error handling
updated backend error handling

1) added exception catchers on each function that talks to backend
and had them reraise exception so that we can get a call stack

2) added break statements whenever an individual result upload or
experiment download fails

Ashish1805/centinel,lianke123321/centinel,iclab/centinel,lianke123321/centinel,JASONews/centinel,rpanah/centinel,rpanah/centinel,rpanah/centinel,iclab/centinel,ben-jones/centinel,lianke123321/centinel,iclab/centinel