Rename test.h into unittest.h

Also code from run_unittest.c is refactored into module unittest.c.

The comparing of log files is done in unittest.c.

A new function is added: execsingle_unittest
which runs a single test and counts the result
(increments nr_of_ok or nr_of_error).

The new function logsummary_unittest prints the number of failed
and passed unit tests.
Implement compare_logbuffer

The function compare_logbuffer compares expected log
content with the content stored in the internal log buffer.
The comparison function returns 0 in case both are equal.
Timestamps are not compared, they are allowed to differ.

Also implemented macro COMPARE_ERRLOG and COMPARE_LOG which calls
compare_logwriter which in turn calls compare_logbuffer.

Remove unittest_adapt_t type and make execsingle_unittest
use the new COMPARE_ERRLOG macro.

Remove the compare_log function from module run_unittest.c