Initial exheres for python-glanceclient

Currently unusable due to missing deps. One thing at a time...
Mask python-glanceclient
glanceclient: argparse only needed on python 3.1
glanceclient: Since only python 2.7, don't need argparse
Initial pbr exheres
pbr: syntax fix
pbr: disable tests

It requires specific older versions of some packages which conflict
with other things in exherbo
polari: Switch to released version.

scm requires unreleased versions of dependencies, and doesn't correctly
fail to build.
polari: Add linguas option
Remove polari scm from mask
polari: Don't install all linguas if none enabled
polari: revert change to disable locales

For now, follow the upstream (and gentoo standard) behaviour of
treating all locales disabled as "install all available locales"