This allows the use of `tini` within even more minimal environments (such as images that are `FROM scratch` with a single application binary `COPY`'d in).
Travis uses Ubuntu Precise, which has CMake 3.8. That version does not
have support for excluding /usr and /usr/bin from the %files% list
(which results in a package that conflicts with the filesystem package
and fails to install).
This commit:
+ Builds on Precise instead of Trusty
+ Adds install tests