Use UNITTEST_LOG_LEVEL in objectstore tests

[tgoyne]

For historical reasons core and sync tests use the UNITTEST_LOG_LEVEL environment variable to determine the test log level, while object store tests used a build time setting. This brings them into alignment on using the env variable, and applies it via setting the default log level on startup in a single place.

The default behavior and log level used on CI should be unchanged.

[coveralls-official]

Pull Request Test Coverage Report for Build github_pull_request_278228

• 46 of 54 (85.19%) changed or added relevant lines in 5 files are covered.
• 51 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.007%) to 91.582%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/realm/util/logger.cpp	28	30	93.33%
test/test_all.cpp	1	7	14.29%

Files with Coverage Reduction	New Missed Lines	%
test/object-store/util/test_file.cpp	1	90.07%
src/realm/object-store/sync/sync_manager.cpp	2	86.9%
src/realm/sync/noinst/server/server_history.cpp	2	67.69%
src/realm/table_view.cpp	2	93.91%
src/realm/query_expression.cpp	3	87.03%
src/realm/sync/noinst/client_impl_base.cpp	3	85.57%
src/realm/util/future.hpp	3	95.81%
test/fuzz_group.cpp	3	48.68%
src/realm/util/assert.hpp	4	87.5%
src/realm/sync/network/network.hpp	7	85.41%

Totals
Change from base Build 1730:	0.007%
Covered Lines:	230351
Relevant Lines:	251523

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💛 - Coveralls

[michael-wb]

Looks good - definitely cleans up the setting of the log level for the tests

[michael-wb]

What about writing the value of UNITTEST_LOG_LEVEL to stderr here, like we did in the makefile, or print an error (with the UNITTEST_LOG_LEVEL) if the value is invalid. Regardless, don't return exit the test on an invalid value.

[tgoyne]

Turns out this is setting the log level for a bit too many things and by default failing checks aren't getting reported. Will need to poke at it a bit more.

[michael-wb]

Turns out this is setting the log level for a bit too many things and by default failing checks aren't getting reported. Will need to poke at it a bit more.

Yeah - IIRC, I think the default logger level was (or at least used to be) "info" and the NullLogger will (obviously) prevent the logger->error() calls from being printed in the tests.
Of note, evergreen was compiling everything with the "debug" log level, not just the object store tests.