Tests for R binaries and packages

[glin]

These are tests to help verify that the R binaries are configured/compiled properly, and that the R packages work.

Specifically, this installs the R deb/rpm in a base OS container, runs some R tests, and uninstalls the deb/rpm. The R tests were copied from https://github.com/rstudio/r-docker, but I only pulled in the tests relevant to r-builds (e.g. BLAS is configured properly, no missing runtime libraries, help pages work).

To test locally, first build the R packages:

# Build R 3.5.3 on each OS
R_VERSION=3.5.3 make docker-build-r

# Or build on a specific OS
cd builder && R_VERSION=3.5.3 docker-compose up ubuntu-1604

# Note: this outputs packages to builder/integration/tmp. To rebuild,
# clear out any existing packages in that directory

And then run the tests:

# Test R 3.5.3 on each OS
R_VERSION=3.5.3 make docker-test-r

# Or test on a specific OS
cd test && R_VERSION=3.5.3 docker-compose up ubuntu-1604

[jonyoder]

Oh, this brings up an interesting question -- should we start signing our installers? Jenkins is already configured with the secrets we need for this.

[glin]

Yeah, I think that'd be great. We still have this issue open: #7

[glin]

Closing - I've redone this and will open a new PR