IMPALA-6317: Add -cmake_only option to buildall.sh

It's sometimes useful to be able to build a complete Impala dev
environment without necessarily building the Impala binary itself
-- e.g., when one wants to use the internal test framework to run
tests against an instance of Impala running on a remote cluster.

- This patch adds a -cmake_only flag to buildall.sh, which then
  gets propagated to the make_impala.sh.

- Added a missing line to the help text re: passing the -ninja
  command line option

Change-Id: If31a4e29425a6a20059cba2f43b72e4fb908018f
Reviewed-on: http://gerrit.cloudera.org:8080/10455
Reviewed-by: David Knupp <dknupp@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

buildall.sh

@@ -183,6 +183,9 @@ do
       LZO_CMAKE_ARGS+=" -GNinja"
       MAKE_CMD=ninja
       ;;
+    -cmake_only)
+      MAKE_IMPALA_ARGS+=" -cmake_only"
+      ;;
     -help|*)
       echo "buildall.sh - Builds Impala and runs all tests."
       echo "[-noclean] : Omits cleaning all packages before building. Will not kill"\
@@ -217,6 +220,8 @@ do
       echo "[-so|-build_shared_libs] : Dynamically link executables (default is static)"
       echo "[-kerberize] : Enable kerberos on the cluster"
       echo "[-fe_only] : Build just the frontend"
+      echo "[-ninja] : Use ninja instead of make"
+      echo "[-cmake_only] : Generate makefiles only, instead of doing a full build"
       echo "-----------------------------------------------------------------------------
 Examples of common tasks: