Backout previous change to the exception handler signature and instead
just log at error level the main part of the redis exception then just
use the original exception handler as-is (at warn level) for the
backtrace. This is a compromise in compatibility insofar as the
backtrace is now at a lower log level, but alerting specifically on
these error strings likely uses the main error strings explicitly logged
before the very verbose backtrace.
The change that Fixesmperham/sidekiq#3673 actually broke any existing
exception handlers due to differences in expected parameter count. This
fixes it explicitly which normally seems like it won't matter but there
are random monitoring gems that install their own sidekiq exception
handlers that I don't want to break.
Extends the `ExceptionHandler` to support multiple log levels and
additional context text in order to use it when the `Processor`
encounters an exception when fetching new work. The added options ensure
that the new behavior is fairly close to the old behavior (same log
level, same fetch error message).
Fixesmperham/sidekiq#3673
