Cleanup: removed separate no-scrape marker file

Changed prefix file format to allow encoding of no-scrape request
using "@ unsupported" directive. Single automatic routing medata
file makes proper synchronization easier to implement and simplifies
overall implementation.

This also eliminated two HEAD requests per remote (due to a bug
original implementation performed HEAD no-scrape file for each
discovery strategy, not once per remote).

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
Fixed wrong RoutingStatusResourceTest initialization sequence

The test was waiting for routing background updates to finish
way too early (before nexus repo manager was started) and was
extremely sensitive to changes auto-routing implementation.

Changed the test to do waiting later during nexus instance
startup. This is still a workaround and the true fix should
wait for a particular event, "repo auto-routing publish state
change" in this case, not for "no backgroup update jobs are
running" as it does now.

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
Cleanup: reconciled autorouting startup and periodic update logic

Automatic routing periodic update logic is now able to initialize
hosted repository prefix path list as needed. No need to do this
explicitly during startup any more.

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>