tests: Error handling improved.

Introduced special error handling functions 'err' and 'err_init' that
must be used in the test scenarios:
* err_init --- error during test initialization; Immediately aborts test;
* err --- check fail error (like check for file existance). Doesn't
          aborts test, instead increases check fails counter which
          will be used in test finalizing.

Also common test template changed. Example --- 00-init.empty.sh test.
tests: Framework refactoring.

Now each test is presented as individual script which can be runned
separatedly from everywhere.

Each test is initialized and finalized by functions from common.sh
script which must be included in the test. It also now accepts some
command line arguments.

Test scenario 00-init-empty may be used as test example. Other
scenarios are temporarily not using current test framework version.
tests: Added retcode check in trut initialization routine.
tests: Logs are moved to separate directory.
gitignore: Updated to new test logs location.
tests: Scenarios 01-03 brought up to latest test framework usage.