crashlog.py: Catch exception from subprocess.
crashlog.py: Catch exception from subprocess.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@355572 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 013af458786e7126bde9632f2df02afc001f9534)

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb