Implement rehash_bucket using a transaction

And use it for long running tests (concurrent hash map drd tests).

This test aborts application in the middle of rehash operation and
checks consistency after restart.

This fixes problem with inconsistent state after crash. In previous implementation
if application crashed in the middle of rehash it was possible that two buckets
(old and new) pointed to the same element. This meant that size could be too big
(some elements could be counted twice). Putting all operations which change list
pointers inside of a transction solves this issue and eliminates requirement
to have 'restore_after_crash' logic.

set_rehashed is done outside of a transaction because otherwise:
- on abort rehashed flag would be rolled back by obj using memcpy instead of
  std::atomic API which could be UB
- some thread could check for rehashed flag and decide that rehash is not needed
  but after that transaction could abort and move elements back

Fail concurrent_hash_map drd/helgrind tets on non-pmem

Add option to enable concurrent_hash_map drd and helgrind tests.
If this option is enabled and TEST_DIR points to non-pmem fail
tests which require pmem and print appropriate error message.

Some tests and examples require clang >= 8.0

Fix installing libpmem-*.rpm

Fix removing pkg-config rpm package

Most rpm based OSes use the 'pkgconf' name,
only openSUSE uses 'pkg-config'.

Replace 'libpmem-*.rpm' with 'libpmem*.rpm'.
It fixes following errors on openSUSE:

error: Failed dependencies:
        libpmemobj1 = 1.7-1.suse1500 is needed by libpmemobj-debug-1.7-1.suse1500.x86_64
        libpmemobj1 = 1.7-1.suse1500 is needed by libpmemobj-devel-1.7-1.suse1500.x86_64

error: Failed dependencies:
        libpmem1 = 1.7-1.suse1500 is needed by libpmem-debug-1.7-1.suse1500.x86_64
        libpmem1 = 1.7-1.suse1500 is needed by libpmem-devel-1.7-1.suse1500.x86_64

Change header_features constant to a function in concurrent_hash_map.

Add test with concurrent_hash_map and pmem::obj::string

(and not libpmem). Add FindLIBPMEM.cmake

Previous behaviour was inconsistent with pkg_check_modules(LIBPMEMOBJ ...)
which only looked for libpmemobj.

Remove using namespace from a header

Install pmdk-debuginfo package

Merge pull request #480 from ldorau/common-fix-invalid-TRAVIS_COMMIT_RANGE-in-case-of-non-upstream-repository

common: fix invalid TRAVIS_COMMIT_RANGE in case of non-upstream repository

Add missing --output-on-failure to all ctest calls

Add valgrind instrumentation to concurrent_hash_map

Add -j$(nproc) to make commands

It fixes the following error on Fedora-rawhide:
 error: Failed dependencies:
	pmdk-debuginfo(x86-64) = 1.7-1.fc32 is needed by libpmem-debug-debuginfo-1.7-1.fc32.x86_64
	pmdk-debuginfo(x86-64) = 1.7-1.fc32 is needed by libpmem-debuginfo-1.7-1.fc32.x86_64

TRAVIS_COMMIT_RANGE is usually invalid for force pushes.
Fix it when used with a non-upstream repository
by setting to the following value: $LAST_MERGE_COMMIT..HEAD

The commit fix the issue with concurrent_hash_map_rehash_0_helgrind test

header_features was only declared (not defined) in concurrent_hash_map header.
This means that (until C++17) it can be used only in places where address of
this constant is not needed. In operator != we access one member of header_fatures
which requrires it to be declared. This only fails for some compilers like clang-9
because rest of the evaluate this expression at compile time (this is a compiler
decision whether to do this at compile time or runtime).

Fix this issue by creating function header_features().

segment_vector: fix typo and doxygen comments

test: fix briefs of concurrent_hash_map test files

Merge back changes from stable 1.7