Remove string libcxx tests which won't be ported

refactor vector private methods

Add get(args) method overload for v.

These tests are either testing deduction guides (which won't be
implemented) or using custom allocator, which cannot be used with
pmem::obj::experimental::string.

Make vector's private methods more generic.
It will be beneficial for implementing vector's modifiers methods.

cmake: refactor the way we add tests to the project

get(args) method forwards args to the objects constructor.

operator= was only assuring that 'this' object was initialized by
calling get. This patch also assures that object from which we
assign is also initialized.

Run tests with PMEM_IS_PMEM_FORCE=1

Merge back changes from stable-1.5

Fix range_snapshotting iterator when snapshot_size == 0

When snapshot_size == 0, no snapshotting should happen. This condition
must be explicitly checked inside range_snapshotting_iterator.

Parameters to iterator should specify range accessible by this
iterator. Before this patch those arguments described the whole
array instead of just the part from start to start + n.

add support for situation, if we don't want to enable valgrind
tool A instrumentation, when test is ran with Valgrind tool B

Change implementation of canonical iterators for tests.

Update a docker image build-dependency.

It got transitioned to libunwind-dev in Oct 2014; there's still a compat
alias but using it gets you shouted at.

New version takes iterator type instead data type. This
allows for more flexible usage. For example it is required for
testing pmem::obj::experimental::basic_string where required
iterator type is const char*.

test: remove libcxx vector tests that won't be ported

Update Valgrind to 3.14

fix README list of flags

vector: add methods which change capacity

test: add internal vector test

Add valgrind instrumentation support

Modify vector_private test to work with Valgrind instrumentation.

Add const methods to pmem::obj::experimental::array. 

Make persistent atomic fix