[#450 YDB#927] Add v63013/gtm9278 test to verify new error messages in read-only database situations - also test YDB#927

This commit adds the v63013/gtm9278 subtest to verify that we get newly added messages in two different read-only database situations:

1. When the client sends a message to an existing gtmsecshr and that message fails to be sent within 4 tries. In this situation, there are two new messages that are seen. The first is a secondary (YDB-I-TEXT) message that the DB Header flush failed and the second is reporting the temporary path that gtmsecshr is using (GTMSECSHRTMPPATH).
2. When the database to be opened was originally thought to be read/write but the read/write open failed but instead a read-only open worked, YDB puts out a new DBFILERDONLY message.

This test also tests YDB#927 (closed) (which it depends on). The initial fix for YDB#927 (closed) (YDB!1215 (merged) in commit YDB@be80269d) turned out to have some issues (see YDB!1218 (merged)) when multiple processes were involved so this test invokes things that previously caused these tests to fail.