Add XML2 package and a few others to r-base-image; remove duplication…

… in R packages targets. (#94)

* Add XML2 package to r-base-image; remove duplication in R packages targets.

* Followup to Corey's comment.

r-client/Dockerfile

@@ -81,19 +81,12 @@ RUN set -eux; \
     [ 0 = `ldd /usr/lib64/R/bin/exec/R | grep 'not found' | wc -l` ]
 
 #
-# Ubuntu R libraries install.
+# R libraries install.
 #
-RUN set -eux; \
-    [ "${DISTRO_BASE_SHORT}" = "ubuntu" ] || exit 0; \
-    . "${PREFIX}/env.sh"; \
-    echo 'install.packages(c("Rcpp", "arrow", "R6", "dplyr", "testthat"), quiet=TRUE)' | \
-      MAKEFLAGS="-j${NCPUS}" R --no-save
-
-#
-# Fedora and RHEL R libraries install.
+# Note repos=... is necessary for Fedora and RHEL.
 #
 RUN set -eux; \
     [ "${DISTRO_BASE_SHORT}" = "fedora" ] || [ "${DISTRO_BASE_SHORT}" = "ubi" ] || exit 0; \
     . "${PREFIX}/env.sh"; \
-    echo 'install.packages(c("Rcpp", "arrow", "R6", "dplyr", "testthat"), repos="http://cran.us.r-project.org", quiet=TRUE)' | \
+    echo 'install.packages(c("Rcpp", "arrow", "R6", "dplyr", "testthat", "xml2", "lubridate", "zoo"), repos="http://cran.us.r-project.org", quiet=TRUE)' | \
       MAKEFLAGS="-j${NCPUS}" R --no-save