Merge stable-1.6 into stable-1.7

Create separate Docker images for stable-1.7 branch

Create separate Docker images for stable-1.6 branch

Add missing pmdk-debuginfo rpms installation

Merge changes from stable-1.6

tests: remove unnecessary #include <libpmemobj.h>

Merge changes from stable-1.5

allocator: remove unnecessary #include <libpmemobj.h>

Including libpmemobj.h causes inclusion of all type macros
which are not needed by C++.

Including libpmemobj.h causes inclusion of all type macros
which are not needed by C++.

Merge stable-1.6 into stable-1.7

Merge back changes from stable-1.5 to stable-1.6

[1.5] Do not check pkgconfig on windows

it might be installed (as part of cygwin).

Backport appveyor update to stable-1.5

... to reduce the Appveyor build time.

... to reduce the Appveyor build time.

PMEM_IS_PMEM_FORCE is not set in tests
and Appveyor build is timed out.

This change is required because of the following issue:
https://help.appveyor.com/discussions/problems/24684-problem-with-vcpkg-wrong-version-on-appveyor
https://github.com/appveyor/ci/issues/3052
which cannot be fixed directly now.

[1.7] Fix compilation of concurrent hash map test

[1.7] Fix void_t declaration.

Update test to new hashmap API introduced in: c67264ae

Extend warning message when valgrind is not found.

Install libpmemobj++.pc in all configurations

Drop libdir from pkgconfig.

Specify we need devel package.

Until CWG 1558 (a C++14 defect), unused parameters in alias templates were
not guaranteed to ensure SFINAE and could be ignored, this implementation
of void_t solves this issue. See: https://en.cppreference.com/w/cpp/types/void_t

cmake: fix tbb detection for distros without tbb cmake integration

There's no binary library to link against.

string: fix memcheck error of uninitialized size field