taskbase: Allow specifying path to ostree repo on command line
taskbase: Allow specifying path to ostree repo on command line

For completeness, then we can be more easily run from any directory;
nothing should be using os.getcwd() or the present outputdir.

tlitovsk/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,projectatomic/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,tlitovsk/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,tlitovsk/rpm-ostree-toolbox,projectatomic/rpm-ostree-toolbox,tlitovsk/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,projectatomic/rpm-ostree-toolbox,tlitovsk/rpm-ostree-toolbox,projectatomic/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,tlitovsk/rpm-ostree-toolbox,maxamillion/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,sujitfulse/rpm-ostree-toolbox,markllama/rpm-ostree-toolbox,giuseppe/rpm-ostree-toolbox,projectatomic/rpm-ostree-toolbox