Merge stable 1.8 into master

Add more defrag tests

Add defrag to concurrent hash map

After introducing defrag() compiltaion of test with 1.8 headers fails.

Set tests' timeout value to 590 secs,
because after 10 minutes the build is considered as stalled by Travis:

"No output has been received in the last 10m0s,
this potentially indicates a stalled build
or something wrong with the build itself."

It's needed to iterate over all internal pointers of basic_string.
It's used in the 'defrag' class for storing all pointers
in the internal list for the defragmentation process.

tests: fix transaction test

detect GDB and disable tests

We did not set counter to a proper value which caused failure on
older std libs (for example in rhel-7.7)

ref issue #469

Add simple hash_map benchmark for opening time

concurrent_hash_map: change implementation of runtime_initialize(bool)

This patch changes implementation to be the same as before
708bd019 (implementation of
runtime_initialize(void) is left unchanged).

The change is needed for backward compatibility with pmemkv-1.0. There, we
called runtime_initialize(true) in a transaction after tx commit (we assumed
there is nothing transactional in runtime_initialize). Introducing a tx
inside new runtime_initialize() results in crash on 1.0

Update PMDK to newest devel-1.8

tests: increase poolsize for enumerable_thread_specific access test

in some runs (depending on thread scheduling) test ended with out-of-memory
error.

It measures mainly runtime_initialize() time.

Fix delete_persistent to be called properly, on object, in ptr test

Add defragmentation feature

Can be used to iterate over all internal vector's pointers.
It's used i.a. in defrag class for storing all ptrs
in internal list for defragmentation process.

Add a defrag class, which holds pointers which will be a subject
of a defragmentation process, using libpmemobj's pmemobj_defrag()

ref. pmem/pmdk#4066

Hash map consistent size feature