build-unit-test-docker: Add libdbus-1-dev

Add libdbus-1-dev to the base image for dbus-1.pc.  This lets us not
hardcode things like system_bus_services_dir.  For example, consider
this meson.build fragment:

dbus_system_bus_services_dir = dependency('dbus-1').get_pkgconfig_variable(
    'system_bus_services_dir',
    define_variable: ['prefix', get_option('prefix')])

This was the intent behind 7a6b382 but the wrong package was added, so
that change is reverted as well.

Change-Id: Ifd2d703122ad545c04ac7e835fd5f8eed1bc8012
Fixes: 7a6b382
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index 81c238b..e690d9a 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -210,7 +210,7 @@
     libc6-dev \
     libtool \
     bison \
-    dbus \
+    libdbus-1-dev \
     flex \
     cmake \
     python3 \