Build wheel cache for venvs

Building a bunch of virtual envs later is going to be tedious if we do not
pre-cache certain annoying-to-build packages.

* tools/build_wheels.sh: pre-build some wheels for annoying package installs
* list distro package dependencies in files/*/venv
* list packages to pre-build as wheels in files/venv-requirements.txt
* install database Python modules when setting up the database

Change-Id: Idff1ea69a5ca12ba56098e664dbf6924fe6a2e47
diff --git a/stackrc b/stackrc
index 386c5d5..ee601a9 100644
--- a/stackrc
+++ b/stackrc
@@ -112,6 +112,11 @@
     source $RC_DIR/.localrc.auto
 fi
 
+# Configure wheel cache location
+export WHEELHOUSE=${WHEELHOUSE:-$DEST/.wheelhouse}
+export PIP_WHEEL_DIR=${PIP_WHEEL_DIR:-$WHEELHOUSE}
+export PIP_FIND_LINKS=${PIP_FIND_LINKS:-file://$WHEELHOUSE}
+
 # This can be used to turn database query logging on and off
 # (currently only implemented for MySQL backend)
 DATABASE_QUERY_LOGGING=$(trueorfalse True DATABASE_QUERY_LOGGING)