CDRIVER-5770 Convert retryable write command construction prose tests to spec tests

[kevinAlbs]

Summary

Resolves CDRIVER-5770. Adds new retryable writes spec tests. Includes fixes to the unified test runner needed to pass tests.

DRIVERS-943 converts "Command Construction" tests into unified spec tests. The original "Command Construction" tests added in SPEC-969 were not implemented in the C driver.

Use single mongos to insert initialData

Fixes an observed test failure:

test file: snapshot-sessions
Result mismatch:
Expected:  [ { "_id" : { "$numberInt" : "1" }, "x" : { "$numberInt" : "11" } } ]
Actual:    [  ]

This matches spec recommendation:

If the topology is sharded, the test runner SHOULD use a single mongos for handling initialData to avoid possible runtime errors.

Use primary read preference to disable failpoints

Fixes an observed test failure inserting initial data:

error: Failed to send "insert" command with database "retryable-writes-tests": Failed to read 4 bytes: socket error or timeout

The failure appears due to using primaryPreferred read preference to disable failpoints. A previous test marked the primary server Unknown, then disabled the failpoint on a secondary instead of the primary. Failpoints are expected to be configured with primary read preference:

The failPoint operation instructs the test runner to configure a fail point using a "primary" read preference

Additional fixes

• Remove bson_destroy of bson_t created with tmp_bson.
• Abort test on failure to disable failpoint, rather than log.
• Create internal MongoClient after possibly modifying test URI to include multiple mongoses.

[eramongodb]

Minor question; otherwise, LGTM.

[eramongodb]

Curious: why a hardcoded serverId vs. pinning via a client session?

[kevinAlbs]

I expect either works. Session pinning only occurs on mongos when using a transaction or using a load balancer. Keeping the hard coding for simplicity.