Add ``--timeout`` option in chisel cut so that users can
specify their preferred limit for each request to avoid
context deadline error [0].

Duration (with unit) should be specified as the argument of
the new option. A timeout of zero means no timeout. Default
timeout is 60 seconds.

Additionally, increase the hardcoded Timeout in the http
client in archive.go to match the default 60 seconds limit.

Fixes canonical#14.

References:
- [0] canonical#14

Pass --real-archive option in go test to run this
test with real archives.

The --real-archive flag specified in archive_test is used
to test real archives and timeout limits. Run these tests
in the github workflow.

This reverts commit 62b704e.