tests: stress: make tests multithreaded
tests: stress: more defensive programming
tests: stress: cleanup previous test on start
cmake: use gnu99 standard
log: remove race in eblob_dump_id_len()
log: simplified logging

Now that we have macro-based eblob_dump_id we can simplify some code
paths.
blob: switch from GNU99 [0] array to C99 []
tests: stress: fail fast on invalid arguments
tests: stress: align items_num on threads_num boundary
tests: stress: bump test version
tests: stress: print test version on start
blob: use 0xhex format for flags
codespell: comment fixes
tests: stress: do not hold global lock too often
XXX