tests: add generalized tags for tests, use them for run-solo tests

tests: add generalized tags for tests, use them for run-solo tests

We have accumulated several scenarios in prod or wishlists
where it would be useful to have a general infra to say yes/no
about a certain test, and potentially make decisions based on that,
for example:

- runs solo (aka 'time-dependent')
- (wishlist) part of quick smoke-test set
- (wishlist) intermittent failure unrelated to timing
- (wishlist) test broken with a multi-worker config in vpp

Refactor the current "run-solo" code to allow for this extension.

Type: test

Change-Id: Ia5b3810e57c0543753c8e0dc4dc0cfb4a30b36ac
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
Signed-off-by: Klement Sekera <ksekera@cisco.com>