[SPARK-9607] [SPARK-9608] fix zinc-port handling in build/mvn

- pass `$ZINC_PORT` to zinc status/shutdown commands
- fix path check that sets `$ZINC_INSTALL_FLAG`, which was incorrectly
  causing zinc to be shutdown and restarted every time (with mismatched
  ports on those commands to boot)
- pass `-DzincPort=${ZINC_PORT}` to maven, to use the correct zinc port
  when building

Author: Ryan Williams <ryan.blake.williams@gmail.com>

Closes #7944 from ryan-williams/zinc-status and squashes the following commits:

619c520 [Ryan Williams] fix zinc status/shutdown commands

build/mvn

@@ -82,7 +82,7 @@ install_mvn() {
 # Install zinc under the build/ folder
 install_zinc() {
   local zinc_path="zinc-0.3.5.3/bin/zinc"
-  [ ! -f "${zinc_path}" ] && ZINC_INSTALL_FLAG=1
+  [ ! -f "${_DIR}/${zinc_path}" ] && ZINC_INSTALL_FLAG=1
   install_app \
     "http://downloads.typesafe.com/zinc/0.3.5.3" \
     "zinc-0.3.5.3.tgz" \
@@ -135,9 +135,9 @@ cd "${_CALLING_DIR}"
 
 # Now that zinc is ensured to be installed, check its status and, if its
 # not running or just installed, start it
-if [ -n "${ZINC_INSTALL_FLAG}" -o -z "`${ZINC_BIN} -status`" ]; then
+if [ -n "${ZINC_INSTALL_FLAG}" -o -z "`${ZINC_BIN} -status -port ${ZINC_PORT}`" ]; then
   export ZINC_OPTS=${ZINC_OPTS:-"$_COMPILE_JVM_OPTS"}
-  ${ZINC_BIN} -shutdown
+  ${ZINC_BIN} -shutdown -port ${ZINC_PORT}
   ${ZINC_BIN} -start -port ${ZINC_PORT} \
     -scala-compiler "${SCALA_COMPILER}" \
     -scala-library "${SCALA_LIBRARY}" &>/dev/null
@@ -149,4 +149,4 @@ export MAVEN_OPTS=${MAVEN_OPTS:-"$_COMPILE_JVM_OPTS"}
 echo "Using \`mvn\` from path: $MVN_BIN" 1>&2
 
 # Last, call the `mvn` command as usual
-${MVN_BIN} "$@"
+${MVN_BIN} -DzincPort=${ZINC_PORT} "$@"