build-unit-test-docker: Add systemd

Add systemd to the base image for systemd.pc.  This lets us not hardcode
things like systemdsystemunitdir.  For example, consider this
meson.build fragment:

dependency('systemd').get_pkgconfig_variable(
    'systemdsystemunitdir',
    define_variable: ['prefix', get_option('prefix')])

Change-Id: I78c4453978c9c3ee1ec513f7a64b6534f9e97235
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
1 file changed