* Get rid of all remaining JUnit 4 usages except in prober & proxy subprojects
Caveat: Test suites aren't yet implemented in JUnit 5 so we still use the ones
from JUnit 5 in the core subproject.
* Fix some build errors
* End-to-end Datastore to SQL pipeline
Defined InitSqlPipeline that performs end-to-end migration from
a Datastore backup to a SQL database.
Also fixed/refined multiple tests related to this migration.
* Upgradle JUnit to 4.13
Removed third_party/junit folder and all usage of the
JunitBackPort class. As a result, third_party is no
longer a Gradle subproject.
Minor code changes were needed to work around an
error-prone pattern: multiple statement in assertThrows'
runnable lambda.
Also third_party/activation and third_party/jsch. These
dependencies are loaded from remote maven repo. The local
copies are not in use.
* Break circular dependency between core and util
Created a new :common project and moved a minimum
number of classes to break the circular dependency
between the two projects. This gets rid of the
gradle lint dependency warnings.
Also separated api classes and testing helpers into
separate source sets in :common so that testing
classes may be restricted to test configurations.
