test: fix vinyl/errinj spurious failure

The failing test case checks that modifications done to the space during
the final dump of a newly built index are recovered properly. It assumes
that a series of operations will complete in 0.1 seconds, but it may not
happen if the disk is slow (like on Travis CI). This results in spurious
failures. To fix this issue, let's replace ERRINJ_VY_RUN_WRITE_TIMEOUT
used by the test with ERRINJ_VY_RUN_WRITE_DELAY, which blocks index
creation until it is disabled instead of injecting a time delay as its
predecessor did.

Closes #3756