build: Do not build selftest binaries for builds without --enable-selftest

build: Do not build selftest binaries for builds without --enable-selftest

Add new for_selftest option to SAMBA_BINARY() and SAMBA3_BINARY()

This allows us to be much more consistent (at least in the core Samba)
and documents clearly why the binary should not be installed.

Not modified are
 - test_lp_load
 - notifyd-tests
 - gendrandperf
 - test* from examples/libsmbclient
 - dbwrap_torture
 - split_tokens
 - locktest2
 - msgtest
 - msg_sink
 - msg_source
 - versiontest
 - rpc_open_tcp
 - test_headers

As these are not tested in selftest so any change would also be
untested.  Of course they probably should be added in a different
MR.

Also not modified (because they are not tests, nor part of the
build system) are:
 - smb2mount
 - notifydd
 - log2pacp
 - debug2html
 - smbfilter
 - destroy_netlogon_creds_cli
 - spotlight2*
 - tevent_glib_tracker

These do however appear to be untested.

For now, the source4 forked client tools are left unchanged:
 - smbclient4
 - nmblookup4

Finally, the heimdal binaries are left as install=False as
they are either part of the build system or end-user tools
that we just don't want to install.  These are however tested.

The motivation is commit like c34ec003b7d45aa4196ff93a0ac29694b25e5309
and da87fa998ab71328f30bcdf5b41aee8675aee48a, which are both totally
correct but are not needed if the selftest is not run on MacOS.

There are likely other platforms or build environments where building
our test binaries is more pain than valuable, see for example also
https://lists.samba.org/archive/samba/2019-November/227137.html

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Isaac Boukris <iboukris@samba.org>
Autobuild-User(master): Isaac Boukris <iboukris@samba.org>
Autobuild-Date(master): Fri Nov 22 11:48:59 UTC 2019 on sn-devel-184