* content: fixed repo upgrade version
Previously upgrade would enable epoch manager and index v2 but would
not set the version of the format itself. Everything worked fine
but it would not protect from old kopia opening the repository.
* ci: added compatibility test that uses real 0.8 and current binaries
* testing: refactored logs directory management
* content: fixed index mutex to be shared across all write sessions
added mutex protection during writecontent/refresh race
* testing: upload log artifacts
* content: bump revision number after index has been added
This fixes a bug where manifest manager in another session for
the same open repository may not see a content added, because they
will prematurely cache the incomplete set of contents.
This took 2 weeks to find.
* manifest: improved log output, fixed unnecessary mutex release
* testing: rewrote stress test to be model-based and more precise
* cli: fixed remaining testability indirections for output and logging
* cli: added cli.RunSubcommand() which is used in testing to execute a subcommand in the same process
* tests: refactored most e2e tests to invoke kopia subcommands in-process
* Makefile: enable code coverage for cli/ and internal/
* testing: pass 'testing' tag to unit tests which uses much faster (insecure) password hashing scheme
* Makefile: push coverage from PRs again
* tests: disable buffer management to reduce memory usage on ARM
* cli: fixed misaligned atomic field on ARMHF
also temporarily fixed statup-time benign race condition when setting
default on the timeZone variable, which is the last global variable.
