[YSQL] Migrations aren't always republished

[frozenspider]

Description

When building Yugabyte, YSQL migrations are copied into build/latest/share/ysql_migrations - but right now cmake doesn't always execute this step, leading to stale migrations failing tests.

Workaround

For now, use ybd <build_type> --cmake-only to guarantees that migrations list is republished.

[frozenspider]

Fixed in a45b3d2

[frozenspider]

Reopened due to cmake -E rm not being available prior to CMake 3.17