Fix race in couchdb_views_tests

[eiri]

Overview

There are a race condition in restore_backup_db_file function between couch_server eviction of an old db updater and a test quering view on restored db file. The query in test can get old record for the updater and then crash with noproc exception.

This change makes restore_backup_db_file to wait until start of the new db updater.

Testing recommendations

The following should pass:

make eunit apps=couch suites=couchdb_views_tests tests=backup_restore_test_

GitHub issue number

Fixes #565

Checklist

• Code is written and works correctly;
• Changes are covered by tests;
• Documentation reflects the changes;

[nickva]

      couchdb_views_tests:backup_restore_test_/0
======================== EUnit ========================
Upgrade and bugs related tests
Application crypto was left running!
  couchdb_views_tests:159: should_not_remember_docs_in_index_after_backup_restore...[0.150 s] ok
[os_mon] cpu supervisor port (cpu_sup): Erlang has closed
  [done in 0.282 s]
=======================================================

+1