[#766] Stop Travis build if a dependency install fails

To do so, I needed to split our ./bin/travis-build in two files, one with the
deps install, and one with the test run. Doing so allows me to use the
"install" directive in Travis, and break the build as soon as something fails
with it.
[#766] Remove redundant datastore_test psql user creation
[#766] Move solr configuration to travis-run-tests

I was unable to run Jetty-Solr's configuration on travis-install-dependencies.
Probably something to do with Bash's "set -e", but I was unable to pinpoint
exactly, so I left it into travis-run-tests. No big deal.
[#766] Use /bin/sh instead of /bin/bash
Merge branch 'master' into 766

Conflicts:
	bin/travis-install-dependencies
Merge pull request #766 from okfn/766-stop-travis-build-when-deps-install-fails

Recurring travis fail `no such option 'with-pylons'`