tests/carp: Rework unicast_v4
For unicast tests, it is sufficient to use wait_for_carp() to verify
the setup is sane. Additional sanity checks are not necessarily
required but can serve purpose for redundancy.
For some unclear reason routed(8) is advertising route to carp BACKUP.
That makes the test flaky. Also routed(8) is marked deprecated and may
be removed from base in the future. Let's just add static route entry
manually for additional sanity checks.
Other noticeable changes:
1. Add atf_check to configuration steps to prevent potential failure
on setup. That helps diagnosing on failure.
2. Shorten the names of jails to improve readability.
3. Prefer `[ifconfig|route|sysctl] -j` over `jexec [ifconfig|route|sysctl]`
to make the lines shorter.
MFC note: At the time writing, routed(8) does not know carp addresses
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tests/carp: make a 0.2 second pause before configuring second jail
for all scenarios where both jails have same priority/advskew. There is a
tiny chance that on both sides carp_master_down() will be executed in
parallel and advertisements will also fly through the bridge(4) in
parallel, thus both sides will switch to MASTER before receiving the
announcement from peer. This makes the test to fail. So far this
flakyness was observed for carp:vrrp_v4 only, but in theory it is possible
for any of the patched scenarios.
Note that this sleep does not prolong execution of the tests, as the first
jail is already configured, and if we slept before configuring the second,
we would sleep less in wait_for_carp().
(cherry picked from commit 27ff90cd3d8d2ac8198f30cbebeefb15a49d41bc)
(cherry picked from commit ad2fff6d6a4d74b6bb9008e447eafc567e8660e0)
