unit: Print D-Bus error message in verbose mode

If g_dbus_setup_private() fails (e.g. a session bus is not available,
and there is no X11 for dbus-launch to work), the tests are silently
skipped.

With this commit, the D-Bus error message is also printed if verbose
mode is enabled. The test is still skipped as before.
core: Add support for graceful shutdown of adapters
shared: Use < for management commands and > for events
lib: Remove current unused management settings helpers
core: Fix setting up discoverable from stored settings on power on
lib: Remove all management settings helpers since they are unused now
tools: Remove redundant include
shared: Remove redundant include
core: Fix includes for mgmt.h and uuid.h
profiles: Fix includes for uuid.h
obexd: Fix includes for uuid.h
tools: Fix includes for mgmt.h
monitor: Fix includes from Bluetooth library
build: Only install old legacy Bluetooth library headers
build: Enable Bluetooth library for distribution builds
doc: Clarify the error codes of some management commands
tools: Fix up testing of discoverable management command
unit: Avoid D-Bus calling _exit() during SDP tests

While running tests, the D-Bus library was set to call _exit() when the
client leaves the bus. This caused the second test to be interrupted
without providing a PASS/FAIL result. This was confirmed by running
test-sdp with DBUS_VERBOSE=1.

This commit disables this behavior, which does not exist on BlueZ
because g_dbus_set_disconnect_function() implicitly does this.
core: Fix remaining references to bluetooth/uuid.h

These headers are not public anymore, so need to use "lib/uuid.h".
plugins: Fix remaining references to bluetooth/uuid.h

These headers are not public anymore, so need to use "lib/uuid.h".