Do not try to run source services when building in a non package wc. This
is the behavior we had prior commit c39c3b8cae
("Cleanup the source services execution code in do_build").
There is no "sane" way to execute the source services in case of a
non package wc build because we cannot export the OBS_SERVICE_PACKAGE
env variable with a meaningful value.
Fixes: #936 ("'osc build --local-package ...' fails with 'not an osc
package working copy'")
3ed9325a15