make check: Fix running from extracted tarball rather than git

Required for Debian packaging support as it by default runs the tests
before building binary packages.
Fix running `make check` when stbt is not installed

Some of the integration tests would fail if stbt was not installed.  This
means that the tests would have been running against (or at least affected
by) the installed version of stbt.  This is bad as the results from `make
check` are then misleading - the installed version may pass but the source
version which you want to check fails.

This commit fixes this issue by taking the sledgehammer approach - do a
`make install` into a sandboxed directory before running the tests.  This
has the beneficial side effect that the integration tests are now also
testing that `make install` works correctly and issues like this are
now unlikely to recur.

This is required for Debian packaging as Debian runs `make check` while
building a package, but is a good idea anyway.
Add support for generating debian packaging

The intention is to set up a Ubuntu PPA to ease deployment onto Ubuntu.

The packages in Debian wheezy (current stable) are unfortunately not
current enough to build and run stbt but it works with Debian testing.
rpm spec file: Fill in Version automatically

With this change the RPM spec file no longer has to be updated with each
release.  Apart from not repeating ourselves this lends itself to more
automation around the release process and the possibility of creating
development RPMs in a continuous fashion using the OpenSUSE Build Service.
rpm: Fix for building rpms for OpenSUSE

OpenSUSE, like Debian but unlike Fedora, expects `libexecdir=/usr/lib`
rather than `/usr/libexec`.  This commit fixes the spec file such that it
can be used to target both OpenSUSE and Fedora.
Add Makefile target obs-publish

Automates pushing stbt updates to the OpenSUSE build service.  The
instructions were going to get a bunch more complicated if we wanted
to add Debian support so this commit automates that process.

This - combined with the change to fill in the rpm spec file version
automatically - also opens the door to the possibility of hooking it into
travis such that we have an stb-tester-master repo so brave souls can run
against git master without having to `make install` themselves.
REMOVEME: Find out why Travis doesn't like this