Reset cros_build_lib.Die so it no longer dumps arbitrary tracebacks.
Reset cros_build_lib.Die so it no longer dumps arbitrary tracebacks.

This was broken via CL:21581; the problem here is that Die historically
never output tracebacks, and now does if there is one sitting in sys.exc_info.

For a demonstration, try:
cbuildbot --remote -p my-nonexistent-project

Note the traceback.  That was never intended, and was regressed in 21581.

Problem is, the TB can be useful in certain cases, and since the regression
wasn't caught immediately, it's possible certain code now relies on it.

Not sure what's best, just posting this CL to kick off that discussion.

BUG=None
TEST=cbuildbot --local -p my-nonexistent-project

Change-Id: Ia6fbf6f839af35d4f640060d69a12a01a044f5dd
Reviewed-on: https://gerrit.chromium.org/gerrit/32104
Commit-Ready: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Reviewed-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>

coreos/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,zhang0137/chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,coreos/chromite,bpsinc-native/src_third_party_chromite