jit-diff handling of errors (e.g., JIT asserts) should be improved

I ran diffs with:
```
jit-diff diff -o c:\diffs -t 4 -a -f -v --test_root c:\gh\coreclr\bin\tests\Windows_NT.x86.Release --core_root c:\gh\coreclr\bin\tests\Windows_NT.x86.checked\Tests\Core_Root -b e:\gh\coreclr2\bin\Product\Windows_NT.x86.checked -d c:\gh\coreclr\bin\Product\Windows_NT.x86.checked
```
It ran all baselines (as far as I know), but two failed with asserts. It then output:
```
Dasm commands returned with total of 2 failures
```
and stopped.

This message is not useful. It should print out the file paths of the *.err files that were generated, capturing the errors.

It should also continue, running the diff compiler as well, so I get as many diffs as possible.