addrmgr: fix intermittent addrmanager_internal_test bug

[kcalvinalvin]

Sometimes the tests in the addrmanager_internal_test will fail with: "addrmanager_internal_test.go: expected to find 5 addresses, found 4"

This is because the generated address with randAddr() may not always generate an address that's routable. If the address is not routable, that address will not be added to the manager when calling AddAddress().

This bug is fixed by creating a new function routableRandAddr() that always creates a routable random address.

[coveralls]

Pull Request Test Coverage Report for Build 8152603231

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 56.776%

---

Files with Coverage Reduction	New Missed Lines	%
connmgr/connmanager.go	2	86.27%

Totals
Change from base Build 8117173129:	0.0%
Covered Lines:	29296
Relevant Lines:	51599

---

💛 - Coveralls

[kcalvinalvin]

To reproduce the bug, you can spam go test in the addrmgr package.

[I] calvin@nixos ~/b/b/addrmgr (master)> go test
--- FAIL: TestAddrManagerV1ToV2 (0.00s)
    addrmanager_internal_test.go:171: expected to find 5 adddresses, found 4
FAIL
exit status 1
FAIL    github.com/btcsuite/btcd/addrmgr        0.039s

This doesn't happen with this PR applied.

[guggero]

Nice fix, LGTM 🎉

[Roasbeef]

LGTM 🧩