There are multiple tests with the same in different directories; add a
unique prefix to test names so that it is clear from the output which
one is running.

Like autotools, use the wrapper script 'run-nm-test.sh' that starts a
separate D-Bus session when needed.

RHEL 7.1 and Ubuntu 14.04 LTS both have this.

https://bugzilla.gnome.org/show_bug.cgi?id=792323

Some targets are missing dependencies on some generated sources in
the meson port. These makes the build to fail due to missing source
files on a highly parallelized build.

These dependencies have been resolved by taking advantage of meson's
internal dependencies which can be used to pass source files,
include directories, libraries and compiler flags.

One of such internal dependencies called `core_dep` was already in
use. However, in order to avoid any confusion with another new
internal dependency called `nm_core_dep`, which is used to include
directories and source files from the `libnm-core` directory, the
`core_dep` dependency has been renamed to `nm_dep`.

These changes have allowed minimizing the build details which are
inherited by using those dependencies. The parallelized build has
also been improved.

This header is already included by "nm-default.h".

Note that:

 - we compile some source files multiple times. Most notably those
   under "shared/".

 - we include a default header "shared/nm-default.h" in every source
   file. This header is supposed to setup a common environment by defining
   and including parts that are commonly used. As we always include the
   same header, the header must behave differently depending
   one whether the compilation is for libnm-core, NetworkManager or
   libnm-glib. E.g. it must include <glib/gi18n.h> or <glib/gi18n-lib.h>
   depending on whether we compile a library or an application.

For that, the source files need the NETWORKMANAGER_COMPILATION #define
to behave accordingly.

Extend the define to be composed of flags. These flags are all named
NM_NETWORKMANAGER_COMPILATION_WITH_*, they indicate which part of the
build are available. E.g. when building libnm-core.la itself, then
WITH_LIBNM_CORE, WITH_LIBNM_CORE_INTERNAL, and WITH_LIBNM_CORE_PRIVATE
are available. When building NetworkManager, WITH_LIBNM_CORE_PRIVATE
is not available but the internal parts are still accessible. When
building nmcli, only WITH_LIBNM_CORE (the public part) is available.
This granularily controls the build.

There are some tests located in different directories which are
using the same name. To avoid any confussion a prefix was used to
name the test and the target.

This patch uses the prefix just for the target, to avoid any
collision that may happen, and uses the `test-` pattern as the
name.

https://mail.gnome.org/archives/networkmanager-list/2017-December/msg00051.html

meson is a build system focused on speed an ease of use, which
helps speeding up the software development. This patch adds meson
support along autotools.

[thaller@redhat.com: rebased patch and adjusted for iwd support]

https://mail.gnome.org/archives/networkmanager-list/2017-December/msg00022.html

We also do this for libnm, where it causes visible changes
in behavior. But if somebody would rely on the hashing implementation
for hash tables, it would be seriously flawed.

Next we will use siphash24() instead of the glib version g_direct_hash() or
g_str_hash(). Hence, the "nm-utils/nm-hash-utils.h" header becomes very
fundamental and will be needed basically everywhere.

Instead of requiring the users to include them, let it be included via
"nm-default.h" header.