Update "Debugging Impala Minidumps" Wiki page

The Wiki page "Debugging Impala Minidumps" is a bit stale and could use some modifications. Specifically:

1. In IMPALA-12125, we added the ability to dump symbols for OS packages that don't have a separate symbols package. Some commercial distributions of Impala such as Cloudera's CDP produce this type of packaging.
2. The documentation for dumping symbols from OS packages references packages from Cloudera's CDH 5.8. This is an old version, and it would be useful for the example to be on a more up-to-date version.
3. The section "Extracting from Jenkins build artifacts" does not seem to be useful anymore.
4. minidump-2-core is definitely a useful workflow and filling in information about it would be useful. In particular, a valuable technique is to use minidump-2-core, then run gdb with the unstripped binary. Examining the stack can yield the query / thread that crashed.